Microcirculation and the relationship between human

(A) on the microcirculation and international experts discussed:
human flesh and blood inside and outside the internal organs of various organs, no one burst, we see the blood flow out of the blood is visible over the body where there where there is blood microcirculation. from the disease etiology, pathology, found that although the incidence of different reasons, but the microcirculation to hypoxia, cell activation and disease occurrence and development of old age the importance of pathology 1. How to improve human microcirculation, activation of cell functions, to prevent diseases and development of life sciences in recent years a hot topic.
microcirculation directly affects the function of state of the oxygen transfer.
micro-circulation and general circulation five characteristics compared:
l, in the property, the micro-circulation is the most peripheral part of the circulatory system,shaiya gold, but also are important components of organs, capillaries, lymphatic capillaries are the most peripheral part of the circulatory system, is the circulatory system.
2, in the form, the micro-circulation that is in common with the vascular, but also the characteristics of organs.
3, in function, the micro-cycle is the cycle path, but also a place for material exchange.
4, in metabolism, microcirculation, both with blood vessels, lymphatic vessels, tissue space such as the common nature of the metabolism, but also to show their real cellular metabolism in the organs of some of the characteristics.
5, in conditioning, well received by the systemic neural and humoral regulation, it is mainly affected by local regulation.
microcirculation is the blood flowing through the small arterioles, through the capillaries, the flow of micro-vein circulation. Its main function is to transport oxygen to tissue cells and nutrients, take away cell produced carbon dioxide and other metabolites. Therefore, microcirculation in the tissue cells to ensure normal metabolism and function play an important role. Many diseases. Such as inflammation, shock, burns, trauma, tumor, etc., have microcirculation, it brings congestion and edema and a series of pathological changes. Therefore, regardless of changes in microcirculation in normal subjects and patients are important. Increased blood viscosity, blood flow is slow, microcirculation will inevitably lead to decreased local tissue perfusion, and hypoxia, acidosis machine humoral factors released to promote red blood cell deformability decreased. Enhanced platelet and erythrocyte aggregation, is all the more increased the formation of blood viscosity.
cancer is common and frequent disease seriously endangering people’s health, microvascular and tumor growth and metastasis are closely related. In recent years, scholars found that the tumor biology and tumor midship diagnosis, treatment and changes in microcirculation have a significant relationship. High pressure and coronary heart disease
obvious a microcirculation, clinical application of microvascular expansion, blood stasis, improve the microcirculation of the way, can improve blood pressure and coronary heart disease and mitigation.
microcirculation basic function is to ensure that the blood perfusion of tissue or organ in order to maintain normal function of Health shoulder blade. As the organization caused by inadequate blood perfusion, pathology, physiological changes are the basis of many diseases, or in the pathogenesis of stages.
micro-thrombosis is an important indicator microcirculation, we found that micro-circulation in coronary heart disease by up to 23 appears microsphere 9%.
microcirculation function, morphology and metabolism in human organs is to maintain the integrity of the important conditions for normal function … … 40 years domestic and international research shows that many diseases are associated with different degrees of systemic or local, acute and chronic Pi microcirculation.
(b) What is microcirculation? microcirculation what function?
the experts directly involved in the cell material information, energy, transmission blood, lymph flow, the body arterioles, capillaries, venules between the blood circulation, called micro-circulation. Microcirculation of the body cells to absorb nutrients, oxygen, and expel the transformation metabolites place. The human body simply can not rely on strength of contraction of the heart directly to the blood perfusion to the 人体各器官 tissue cells, must rely on some of the capillary microcirculation of the heart beat out of sync with the self-discipline sport in the blood for the second adjustment, the second infusion, so microcirculation in the medical metaphor for the human body to the “second heart.”
(c) What are the characteristics microcirculation?
1, micro-circulation in the capillaries is very long, about 9-1I million km, can Two weeks and a half around the earth, found in the human body from different angles everywhere.
2, circulating blood vessels is very large, about 30 billion.
3, micro-circulation of the blood vessels wall is very thin, only one per cent of ordinary white paper, white out the material and help, the connection of major blood vessels, the expansion and contraction without aortic capacity.
4, capillaries are very thin, only a twentieth of human hair.
5, capillary lumen pressure is low, pressure difference, the average pressure of normal micro-circulation of about 20 mm Hg.
6, capillaries have sphincter, arteriovenous anastomosis between the traffic branch, the formation of arteriovenous short circuit.
(d) What is microcirculation? of the consequences?
capillary microcirculation is to change shape and flow After the morphological changes induced functional changes in microcirculation of blood vessels if the deformation of blood vessel blockage blocked, the resulting organs and tissues, cell ischemia, hypoxic cell necrosis, resulting in lesions. Microcirculation unimpeded all diseases are not students, microcirculatory disturbance may cause the following consequences: 1, relative or absolute lack of blood volume; 2, metabolic disorders, so that tissue hypoxia, acidosis produced a series of serious results; 3, visceral involvement;
4, of a serious occurrence of disseminated intravascular coagulation.
(e) affect human microcirculation What are the factors?
1, pressure, depending on whether it is normal blood pressure, low blood pressure, heart blood volume will decrease;
2, depends on the cardiac and vascular blood circulation within the effective blood volume is normal;
3, resistance, the main decision vascular tone, blood viscosity and chemical composition;
4, emblem of blood vessels, capillaries deformation.
(6) Why is micro-circulation - the body’s second heart?
China from the early 50s on the establishment of the Society of Microcirculation - Chinese Second Military Medical University. Microcirculation Society of China Vice President - Irreversible said: Microcirculation will trigger the body 414 kinds of diseases and 33 kinds of malignant tumors, it is the source of all diseases.
micro-arteriole circulation is fine by the capillary network to the venous blood circulation between these dense network of small blood vessels in the formation of the body’s blood supply channel environment, its basic functions mainly to achieve blood and tissue cells material exchange. Complete metabolism.
wonderful human body is a complex organism, limited only by the contraction of the heart is unable to carry blood to the heart within the cell, but must rely on their own micro-pan control rhythmic activity , and heart rate are not synchronized. Has its specific rules, such capillaries play a second role in regulating blood into the body of the “second heart.”
with age, the blood viscosity increases, blood flow slows down, blood in the capillaries may occur stasis or even blocked, the human body pain, cold , numbness, and many other symptoms, most are due to microcirculatory disturbance caused. Only in time to clear the blood vessels, excluding microcirculation, is an important way to get healthy. Therefore, the image of rebel scientists cycle is referred to as the body’s “second heart.”
　

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http://shaiya15.pixelblog.com/2010/04/19/microcirculation-and-the-relationship-between-huma/

Microcirculation in insulin resistance and diabetes: more than just a complication

The microvascular bed is an anatomical entity which is governed by specific, highly regulated mechanisms which are closely adapted to the specific funtion of each vascular segment. Among those, small arteriolar vasomotion and capacity of small vessels to constrict in response to physical and humoral stimuli play a major role. Other processes of importance for the adequacy of nutritive perfusion are haemorheological properties of whole blood and red cells, adhesiveness of leukocytes and capillary permeability. This review provides some description of these phenomena, how they impact on organ function and how they appear in diabetes.

Metformin, as a unique example among the drug arsenal, exerts various effects preferentially at the level of smallest vessels (arterioles, capillaries, venules). This review summarises our actual knowledge and includes several new data showing its high potential for reducing microvascular dysfunction. Most of these unique properties have also been demonstrated in non-diabetic animals or humans, suggesting they are intrinsic to the drug and not secondary to diabetic metabolic improvement. A particular focus is put on the relevance of metformin's capacity to stimulate slow wave arteriolar vasomotion and improve functional capillary density, whereby nutritive flow can be re-established.

Finally, the implication of microcirculation in other aspects of insulin resistance and diabetes, such as macroangiopathy and metabolic control, is discussed and strengthens the concept of a broad involvement of microvascular dysfunction in these diseases as well as the potential interest of introducing adapted treatment early in the history of a patient's diabetes.
　

a brief description
The vascular bed can be grossly divided into three main entities: large (macro) vessels, medium (resistance) vessels and small (micro) vessels. Whereas the former are essentially conduit vessels, resistance vessels (diameter 100-500 mm) are primarily involved in the regulation of blood pressure, while the microvascular bed represents the so-called “nutritive” structure. Microcirculation comprises small arterioles, which branch in a tree-like manner into segments of decreasing diameter down to the 5 mm capillaries. These are organised into units, each unit comprising about 15-20 capillaries which depend on a same feeding terminal arteriole [1Berg BR, Cohen KD, Sarelius IH. Direct coupling between blood flow and metabolism at the capillary level in striated muscle. Am J Physiol, 1997, 272, H2693-H2700.

In view of the repetitive branching of the vascular bed, pressure in the narrow vessels is very low, which has evident consequences for blood flow, in particular for haemorheological properties of blood cells.

The microvascular bed therefore represents an entity which is completely different from the macrovascular bed, due to different physiological functions with accompanying specific regulatory mechanisms
structural and functional specificities
The main role of microcirculation is to deliver fuel and nutrients to remote cells as well as to exchange waste products with the surrounding tissues. These aspects are also interrelated since the degree of vessel permeability is not only dependent on the vessel wall structure (tight or moderate barriers vs fenestrated vessels) but also on the prevailing hydrostatic pressure across the arteriolar to venular segment. In other terms, the level of arteriolar response to venular tone (in addition to other factors) also dictates blood tissue exchange capacity.

Marked heterogeneity is found among microvascular endothelium, according to the tissue but also within an organ according to the vessel segment within the branching vessels.Pronounced differences in vessel wall structure are observed since smooth muscle cells tend to diminish with decreasing arteriolar diameter, whereas capillaries are only composed of one single endothelial cell layer apposed onto the capillary basement membrane. This is accompanied by adaptive changes in biochemical mechanisms: for example it has been suggested that vasodilatation becomes less dependent on nitric oxide (NO) but more on endothelium-derived hyperpolarising factor (EDHF) with decreasing arteriolar diameter. The reactivity to various agonists is also varying according to the arteriolar segment under study . On the other hand, physiological permeability is strictly limited to the venular end of capillaries. Such examples illustrate the heterogeneity of the microvascular bed and how structure, function and mechanisms are remarkably interrelated. Diabetic microangiopathy is the sum of multiple defects affecting blood cells, their interactions with the vessel wall, the reactivity of the vessel wall and its anatomical structure. In the following sections some mechanisms which are specific of microvascular physiology will be highlighted for their importance in clinical pathology (especially in diabetes) and some unique and direct effects of metformin will be described.

Vasoconstriction is not necessarily bad!
Watching the microcirculation in situ reveals to the new investigator a picture of constant changes in blood flow within some seconds: filled capillaries coexist with “empty” ones, periodic flow (fluxmotion) is seen as well as sudden changes in flow direction. Such a pattern gives the misleading impression of a chaotic, uncontrolled situation; however this picture in fact just reflects an extremely complex but finely regulated distribution of microflow where amount, velocity and direction of flow permanently adapt to local needs. Obviously this is only made possible due to very specific crosstalking of metabolic, physical, humoural and nervous mechanisms operating in smallest dimensions. In the microvascular bed, therefore, not quantity but distribution of blood is the primary determinant.

That vasoconstriction is in the heart of these processes might at first sight sound paradoxical. Indeed most literature on vascular haemodynamics and reactivity deals with dilatation. While it is indeed of utmost importance in large vessels (amount of blood), the microvascular bed must prevent excessive blood entering the tiny vessels, thereby avoiding capillary hypertension and increased permeability. It is indeed noteworthy that, in sharp contrast to large vessels, the main physiological mechanisms governing the adaptation of flow to local factors (metabolic needs, transmural pressure) rely on constriction of the arterioles, eventually venules .These are: a) the arteriolar myogenic response, whereby transmural pressure such as in exercising muscles is transmitted to the vessel wall, b) the venoarteriolar reflex, whereby signals from the venular end induce arteriolar constriction to prevent capillary hypertension and c) precapillary arteriolar vasomotion.
The myogenic response adjusts the tone of the small terminal arterioles within a narrow range around normal blood pressure All three mechanisms participate, at various times and to a variable extent, to the adaptive regulation of nutritive flow. The daily physiological stimuli to which microcirculation must respond are mainly local tissue metabolic needs and physical changes such as upright positioning. In the legs, the latter will induce an increase in hydrostatic pressure, to which some sensors in the veins will signal the arterioles to constrict. Thereby capillary hyperperfusion and subsequent hypertension are prevented . This crucial phenomenon has been found deficient in both types of diabetes and has become famous as the “haemodynamic hypothesis”. It is enhanced in the presence of neuropathy . The number of daily postural changes points to the potential importance of this phenomenon, which appears to be deficient very early in the disease. The capacity of the arteriole to constrict is crucial, since venous hypertension will cause increased filtration and aedema if not compensated for by a reduction at the inflow level, i.e. the arteriole. Conversely, a minimal capillary venous pressure is a requisite for capillary perfusion. Diabetes, in particular in its early phase, is characterised by a hyperdynamic circulation linked to insulin resistance and several investigations have found abnormally elevated blood flow in early periods of diabetes. However, it must be realised that these measurements are usually performed with techniques whose accuracy does not allow to follow-up nutritive flow. Indeed it has been shown that for its main part this increase in organ flow occurs through dilated shunt pathways, whereby true capillary flow is reduced. It is thus crucial that arterioles keep their capacity to constrict to prevent maldistribution of blood flow and divert blood into the nutritive pathways. A more detailed overview on this specific concept can be found in a dedicated review.

Physiology/pathology
When microcirculation is observed in vivo , most tissues exhibit rhythmic changes in arteriolar diameter, the so-called vasomotion phenomenon. The typical physiological vasomotion is a slow-wave, high amplitude variation in diameter with a frequency of 1-10 Hz. Its meaning has been a matter of many debates but the fact that it is easily observed in most healthy organs and disappears in a number of pathological situations supports a physiological role for vasomotion. In particular, slow-wave vasomotion has been postulated to fill capillary units in an alternating fashion in order to economize the amount of blood flowing through. Indeed, would all capillaries be permanently blood-filled, there would be no further reserve for covering increased metabolic needs. By doing so, vasomotion therefore also induces some pressure waves which help blood flow through narrow capillaries under prevailing conditions of low pressure. Moreover these waves may well be transmitted to adjacent lymphatic vessels and stimulate the lymph pump. Indeed in vivo examinations show that, at any instant in a resting skeletal muscle, neighbouring capillary units are alternatively filled with whole blood (red cells), leading to an estimate of a permanent 50% perfusion of the whole capillary bed in muscle. The advantages of this chaotic flow pattern over constant flow have been evaluated.

Most investigations have shown that slow-wave vasomotion requires the initiation of arteriolar constriction, followed by oscillations of the membrane potential . The underlying mechanisms are still far from elucidated, in particular because the hypothesis of specialised pacemaker cells or precapillary sphincters have never been convincingly demonstrated. Recent studies have pointed towards a role for chloride channels, without precise subtype identification .

Arteriolar vasomotion is blunted in various pathological situations, in particular diabetes. Investigations in both experimental and clinical diabetes have shown its rapid disappearance . Hyperinsulinaemia, possibly via its vasodilating action, also opposes vasomotion. When hyperglycaemia is raised concomitantly, however, vasomotion is stimulated. However, in streptozotocin (STZ)-diabetic rats this effect, which might be of high physiological importance, is blunted.

In humans, 47% of diabetic patients without and 82% with neuropathy showed impaired slow-wave vasomotion, a defect appearing very early and correlated with sympathetic dysfunction . This defect has also been described in the leg skin and suggested to be causally involved in the diabetic foot complication . The importance of preserving arteriolar vasomotion under critical perfusion has been illustrated by its influence not only in muscle itself but also for protecting adjacent tissues.

Haemodynamic effects of metformin
Metformin does not directly affect large vessel tone unless using non-pharmacological drug concentrations. However metformin has been shown both in vitro and in vivo to improve vascular reactivity to the endothelium-dependent vasodilator acetylcholine in insulin resistant rats; this effect was independent of the accompanying metabolic improvement. Similar data were obtained in uncomplicated type 2 diabetic patients when using forearm plethysmography. The hypotensive effect of arginine, as an indicator of vasodilation, was potentiated by metformin in newly diagnosed type 2 diabetics free of macro- and microcomplications . In contrast, metformin has the unique capacity of stimulating or restoring arteriolar slow-wave vasomotion. In line with the fundamental aspects (see above) topical application of metformin to the normal hamster cheek pouch (to eliminate possible systemic interfering effects) induced a slight constriction of arterioles, which was accompanied by enhanced vasomotion (Fig 1).

In normal animals, metformin restored vasomotion in the recovery phase from haemorrhagic shock and most drug-treated animals survived. When insulin was applied topically in mildly diabetic hamsters, vasomotion was reduced as expected and restored by coadministration of metformin. In experimental diabetes, metformin restored blunted vasomotion in both mild (Fig 2)and more severe diabetes . Investigations on lymph flow have shown a stimulating effect of metformin possibly explaining the reduction in albumin retention in metformin-treated type 2 diabetic patients and the drastic inhibition of cyclic aedema.

Experiments performed either in vitro or in vivo (data not shown) failed to reveal any effect of metformin on NO production as a possible explanation for the tendency towards stimulation of vasomotion. Conceivably, inhibition of the relaxing factor EDHF in small vessels might be a possible mechanism but this can hardly be discriminated in vivo . Using microelectrodes implanted in situ into arteriolar walls of the hamster cheek pouch, topical metformin was found to depolarise cell membranes by a mean of 5 mV, in agreement with a trend towards constriction (Bouskela, unpublished data). Many different ionic channels could be responsible for the constrictive effect but recently we could show that, in line with data in hepatocytes, the effect of metformin could be inhibited by chloride channel blockers (manuscript in preparation); this supports the concept that these ionic channels may indeed underlie arteriolar vasomotion and that this mechanism might apply to metformin.

Blood rheology/cell adhesion
Increase in plasma and whole blood viscosity, reduction in erythrocyte deformability and enhanced aggregation are established features in diabetes albeit their causal implication in microvascular disorders remains controversial. At the least these haemorheological modifications complicate passage of blood cells through narrow capillaries and slow down blood transit. At the worst, they obstruct the capillary lumen in a manner depending on the ability of erythrocyte aggregates to disintegrate. In situations of shutting-down of capillary pressure this may become crucial, more so if the capillary lumen is reduced. Although not a universal finding, capillary narrowing has indeed been described in diabetes. This could be due to thickening of the capillary basement membrane, a phenomenon found early in most tissues and which rapidly follows hyperglycaemia. Conceivably, thickening of the endothelial glycocalyx could reduce internal capillary diameter as well. This would then further impair red cell velocity and flux and subsequently reduce oxygen delivery by up to 60% despite resting blood flow.

Another yet unresolved question is the importance of leucocyte adhesion as a process of capillary plugging. An increased number of slowly rolling with some even adhering to the capillary walls is a common observation in the diabetic microcirculation. This could be due to an increased expression/activity of adhesion molecules such as ICAM-1 or VCAM-1, mostly as a result of prevailing glycation or inflammation. This concept is highly emerging and many recent studies have shown that insulin resistance and diabetes are characterised by elevated levels of C-reactive protein, interleukin-6 and TNF-α as a sign of inflammation. The case is amplified when endothelium is glycated.

Haemorheological effects of metformin
Red cell rheology has been studied both in vitro and in vivo : positive data on erythrocyte aggregation and/or deformability have been reported, although with discrepant findings according to the drug concentrations or to in vitro vs in vivo tests. Better cell deformability fits with the improvements in membrane fluidity induced by metformin .

In vitro , monocyte adhesion to glycated endothelium is strongly inhibited by metformin, via a reduction in the expression of the adhesion molecules (cf. Mamputu et al. , this supplement). In vivo , metformin treatment of hamsters submitted to haemorrhagic shock cleared the capillary bed from adhering leukocytes and thereby maintained an almost normal capillary flow . Post-ischaemic reperfusion is another situation where leukocytes stick to capillary walls: as shown in Fig 3, the degree of adhering white cells was much reduced in metformin-treated animals.

Nutritive blood flow
As explained above, within a large physiological range, microvascular flow is much more regulated by various components of flow distribution than by amount of flow. Variations in capillary tube hematocrit, erythrocyte velocity or countercurrent flow are just some of the very characteristic mechanisms whereby nutritive flow is tightly regulated. Capillary recruitment can serve as a first aid mechanism in the event of elevated needs and arteriolar vasodilation can serve as a second process if required. This is typically seen with insulin. Thus the number and degree of cell flow in the capillary bed is a prime determinant; it is termed “functional capillary density” and can be quantitated in situ by calculating the total length of whole blood-filled vessels in a given area under the intravital microscope. Finally it is a mixed quantitative and qualitative estimation of nutritive flow. It is particularly important in situations of sudden elevations in perfusion needs such as in acute exercise or during a post-ischaemic tissue reperfusion period (the no-reflow phenomenon). A good illustration is given by experiments relating functional capillary density to survival from haemorrhagic shock.

In basal conditions we found a 50% reduction in functional capillary density in diabetic animals (Fig 4). In human diabetics, the situation may even be worse, due to a capillary rarefaction in the presence of hypertension, which affects most patients. Such a combination would severely increase the diffusion distance of oxygen and glucose from capillaries to target cells. In post-ischaemic situations, capillary recruitment is the main determinant of early reperfusion and, accordingly, the clinical test of post-occlusion reactive hyperemia (cuff) serves as an indice to evaluate the degree of vascular impairment in man. This test has repeatedly revealed defective vascular reactivity in type 2 diabetic patients, even in the absence of vascular complications. Absence of normal reactivity severely limits flow reserve capacity.

Effects of metformin
As illustrated in Fig 4, chronic treatment with metformin partially compensates for the reduction in basal functional capillary density in diabetic animals. Obviously this beneficial effect was linked with a basal drug-induced constriction occurring simultaneously in both arteriolar and venular segments.

In post-ischaemic recovery studies, metformin remarkably restored capillary perfusion under haemorrhagic shock conditions, which may explain the high rate of surviving animals in the treated group. In mild diabetic animals, post-ischaemic nutritive flow as estimated by functional capillary density was also improved (Fig 5). Noteworthy these effects have been also seen with very low doses of metformin (data not shown). These results support the notion that the main action of metformin must be located at the terminal arterioles and then manifested primarily by an increase in capillary perfusion. This again may likely be explained by activation of arteriolar vasomotion (see above). This hypothesis is further corroborated by experiments performed in normal as well as in diabetic rats where blood flow was measured using various tracers of different size, allowing some discrimination between arterioles and capillaries (J Rapin and N Wiernsperger, unpublished data). Although both indicators showed flow elevation, the tracer used for capillary flow was clearly more augmented than the one for arterioles. The data for the capillary flow are shown in Fig 6. This increase, which occurred similarly in normal and in diabetic rats, was confirmed in other tissues: it occurred in the rat liver (same study), intestine and pancreas, as well as in human adipose and uterine tissue. In post-occlusion tests in humans, metformin improved the peak flow in both normal and arthritic, non-diabetic patients .

Vascular permeability
Permeability is another hallmark of the microcirculation: the intrinsic level of permeation of small vessels is highly variable throughout the body, ranging from very permeable in the splanchnic bed to very tight blood-tissue barriers in organs like brain or retina. Again these structures are adapted to the respective functions of specific tissues and organs. Chronic hyperglycaemia, in particular when advanced glycation endproducts are formed provokes permeability, i.e. extravasation of proteins. The latter may accumulate on the abluminal side and thicken the capillary basement membrane. Hyperpermeability is more particularly known in diabetes in the kidney (micro/macroalbuminuria) and in the retina (proliferative retinopathy exsudates, macular aedema). Increased permeability is postulated to play a key role in initiation or aggravation of diabetic microangiopathy.

Effects of metformin
In diabetic hamsters basal increased permeability was reduced by metformin. In diabetic patients, microalbuminuria was also reduced. Albumin retention was shortened by metformin in the lymph compartment of type 2 diabetic patients. However this property has also been demonstrated in non-diabetic situations: in animals, post-ischaemic cheek pouch permeability was drastically inhibited as shown by a remarkable reduction in the number of leaks (Fig 7). This corroborates earlier findings in peripheral and in brain ischaemia-induced aedema formation. Finally, lower limb aedema disappeared in most women suffering cyclic aedema after 6 weeks'treatment with metformin. Although the exact mechanisms of permeability inhibition by metformin have not been examined yet, beneficial remote effects on hydrostatic pressure due to the venular constriction may be involved.

Additional considerations on metformin effects and their clinical relevance
Microcirculatory effects of metformin are only part of its pleiotropic actions on blood, vessels and related phenomena. However microvascular effects of this drug make it a unique tool because they are selective for this anatomical entity, which is not known for any other drug.

Moreover, they occur independently of the metabolic actions of the drug and therefore apply in a very general way. In view of the crucial importance of microflow, its use to prevent or improve vascular disorders in prediabetes and diabetes appears particularly beneficial. The positive effects exerted by metformin on small vessel regulatory processes are also observed at concentrations equivalent or lower than those required for the metabolic actions. This means that they remain valid even when plasma concentrations fall between daily tablet intakes. They would also apply to cases where metformin is only used as a combination therapy.

On the other hand, we largely ignore what is the reversibility potential of disorders in diabetic vessels according to the severity and/or duration of the disease. Clinical research over the last decade has clearly established that most of the dysfunctions described in detail in this article can be revealed very early in the course of the disease. Especially the pioneering work of J Tooke and his group has shown that many disturbances are already present in states of normoglycaemic insulin resistance, such as IGT or acromegaly. Recent studies have largely corroborated this notion, suggesting that hyperglycaemia is possibly exaggerating disorders which are largely preexisting, albeit not clinically manifest. Should this be further confirmed, as it appears today, it would mean that what is known as diabetic microangiopathy is a disturbance requiring very early intervention, ideally when most troubles are still at a functional level, before structural changes would hamper or prohibit therapeutic drug efficacy.

As an example, the beneficial effect of metformin on microangiopathy in the UKPDS might have been more obvious if its introduction would have occurred earlier in the history of the disease.

Microcirculation in diabetes: its meanings
Actually, microangiopathy is considered as a typical complication of diabetes affecting mainly the eye, the kidney, the nerve and the foot for reasons that are largely unravelled. Diabetic microangiopathy in its clinical presentation is a resultant of haemodynamic defects and anatomical changes of the small vessel walls. The latter are attributable to structural modifications affecting the luminal side (glycocalyx) and the abluminal side (smooth muscle cell proliferation, protein deposition crosslinking through glycation endproducts, etc.). The respective roles played by the more haemodynamic characteristic changes of microvessels in diabetes vs the more structural ones are difficult to distinguish as they are likely intertwined. Nevertheless, when considering the fundamental role played by the microvascular bed throughout the body, some aspects of which have been detailed here, the participation of functional microvascular disorders must also be considered. Indeed, we must be aware that microcirculation is potentially involved in such a disease, at least at three levels: macroangiopathy, microangiopathy, metabolism. As such, microcirculation is an integral part of microangiopathy, which however does not totally explain the clinical development of diabetic microvascular complications. However, we will briefly analyse how functional microvessel haemodynamic defects could be linked to insulin resistance and be involved in its development towards diabetes and its complications.

Microcirculation in diabetic micro and macroangiopathy
Very little is known about the interrelationship between functional and structural changes in diabetic small vessels, as well as about possible pathological thresholds. Indeed, functional defects are known to occur very early in the course of diabetes. It is noteworthy that most metabolic states characterised by insulin resistance – but without fasting hyperglycaemia – are also presenting microcirculatory disturbances (obesity, prediabetes ageing, smoking, thalassemia, low birth weight, postsurgery, etc.). These changes will not, however, translate into microangiopathy such as retinopathy or nephropathy if diabetes does not appear. On the other hand, chronicity of these disturbances may generate adaptive and finally deleterious constitutive changes in the microvessel walls. The latter, as for example the very early occurring thickening of capillary basement membrane, may in turn limit their vasoreactive capacity; as a consequence, opening of arterioles and recruitment of capillaries may become deficient in functional hyperaemic states. On the contrary, vasoconstriction may also be insufficient: for example in early diabetic stages, several tissues show exaggerated blood flow, which precedes retinopathy and nephropathy. Impaired vasoconstriction may favour capillary hyperperfusion and permeability.

Another argument for a partial role of haemodynamic defects in diabetic microangiopathy is the failure of even strict metabolic control to completely inhibit the small vessel complications . These findings strengthen the need for additional therapeutic approaches, particularly in type 2 diabetes, where many factors other than hyperglycaemia are likely to be involved (hyperinsulinaemia, insulin resistance, dyslipidaemia, hypertension, etc.). Thus, in an animal model of type 2 diabetes, changes in coronary arteriolar structure and function were linked to diminished flow reserve before the appearance of fasting hyperglycaemia. Blood hyperviscosity and erythrocyte rigidity are another problematic component of microcirculation which are able to impair blood passage through the capillary bed. Clearly more research is needed to discriminate the respective roles of functional and structural changes in microvessels.

Large vessels have mainly a supplying role but are the site of the most dramatic, life-threatening accidents in case of atherosclerotic, haemostatic or spastic vessel occlusion. However, their consequences are found downstream of the injury, in particular when reperfusion occurs, namely in the microvascular bed . Fortunately there is now a growing awareness that microcirculation is a key player in macroangiopathy, which can be causal of -or subsequent to- large vessel accidents.

Microcirculation in metabolic control
Glucose homeostasis is the resultant of its production and utilisation. Insulin resistance in peripheral tissues such as skeletal muscle relies on deficient glucose uptake and glycogen storage. Despite immense efforts, the exact mechanisms of insulin resistance are still to be defined. Conceivably, hampered delivery of glucose or insulin (timely and/or quantitatively) could be another factor explaining postprandial defects underlying insulin resistance. In this period, a maximal glucose amount must reach muscle cells within a relatively short time to be stored as glycogen; a brief look at the anatomy of skeletal muscle cells reveals capillaries lying between muscle fibres, each one diffusing to several surrounding fibres and insulin-sensitive glucose transporters located in the vicinity of the capillaries. It is easy to understand that if there is a defective capillary perfusion or recruitment in this metabolic period, glucose/insulin delivery will be affected.

Conceivably, then, functional microangiopathy could be an integral part of the metabolic syndrome, as proposed by some authors. Usually tissue metabolism and local microflow are tightly coupled, in such a way that flow adapts to the metabolic demand of the surrounding tissue. However, this relation may be bidirectional and, although the definitive proof is still missing it has been increasingly suggested that, conversely, maladapted arteriolar reactivity may impair nutrient delivery and lead to or aggravate insulin resistance. This recent hypothesis is further supported by several observations showing microvascular dysfunctions very early in the development of insulin resistance/diabetes. In the subsequent worsening of insulin resistance towards diabetes, this factor may even become increasingly important.

Conclusion
In conclusion, microcirculatory defects could be viewed as one factor involved at various stages in both metabolic and angiopathic aspects of diabetes (Fig 8).

Functional disorders of small vessel haemodynamics are likely involved in the worsening of metabolic disorders (in particular insulin resistance during postprandial periods) as well as of structural microvessel modifications leading to nephropathy and retinopathy when hyperglycaemia becomes superimposed.
　

This article comes from:

http://www.em-consulte.com/article/80241

A SIMPLE METHOD FOR STUDY OF MICROCIRCULATION IN ALBINO MOUSE EAR WITH LIGHT MICROSCOPE

Microcirculation in a dynamic state in vivo was stud¬ied earlier using preparations like rat or rabbit mesentery(Animal mesenteric,Animal mesenterium,Animal caul,mesenterium,caul,Animal mesenteric Microcirculation,Animal mesenterium Microcirculation,Animal caul Microcirculation,Mesentery microcirculation, Animal Mesentery Microscope, Animal Mesentery Microcirculation), bat wing, hamster cheek pouch, rat brain and meninges, rabbit ears, frog tongue and foot and human nail bed, bulbar conjunctiva1-3. We screened other tissues to study microcirculation under light microscope with trans-illumination. Frog mesentery mounted on a slide had to be kept continuously moist. Pedicles of rat or mouse mesentery could not be spread over the slide to be covered with a glass cover slip. The fat surrounding mesenteric vessels restricts the visibility of small vessels.
Microscopic study of microcirculation in ears of ho¬mozygous hairless (nude) mouse was first introduced for studying scald burn and ischemia4,5. This breed is not available in all laboratories. Some immobilized the hairless mouse on a plastic holder, with the ear projecting through a slit and attached to a frame6. Microcirculation in hairless mouse is a common ex¬perimental model in several chronic quantified stud¬ies in Plastic & Reconstructive Surgery on wound healing, effects of burns, ischemia and thrombosis with sophisticated techniques of video study and intravital bright-field video microscopy7.
We describe here a simple method, using albino mouse readily available in laboratories for continu¬ous observation of microcirculation in its ear.
Albino mice (Swiss) 25 -30 g were anaesthetized with pentobarbitone sodium 40 mg/kg, i.p. When the mouse was lightly anaesthetized, a commercially available depilatory cream was applied to both ears as a thick layer to remove hair, which interferes in the field of observation. After 20 min the cream was thoroughly wiped off with a tissue paper from the ears. The anaesthetized mouse was now placed prone to occupy a glass slide (Fisher 74 mm x 50 mm), with head turned to one side (Figure 1). One of the ears was fixed flat to the slide with clear transparent ad¬hesive cello tape. The slide was now placed on the microscope stage of a light microscope and viewed by trans-illumination from below with an illuminator.
Olympus microscope with magnifications 'x100' or 'x 400' was adequate for routine study. Oil immersion objective to obtain magnification of 'x1000' was also used as the ear was covered with cello tape. Drugs for study can be given intra peritoneal or into the tail vein. With aseptic precautions, the same mouse can be studied repeatedly.
To monitor continuously a single field for the effects of drugs given intravenously, the jugular vein was cannulated first before placing the mouse on the slide. The procedure described by Popovic et al 8 was modified and followed. The anaesthetized mouse was placed on its back on an operation board under an illuminated magnifier. The skin over the front of the neck was excised to expose the jugular vein. The full and distended vein will shrink with any attempt to clean it. Hence, Ethicon 4/0 thread with an atraumatic needle was passed underneath the vein without dis¬turbing it, for two ligatures, one above to block the flow from cranium and the lower one to ligate the cannula over the vein on the cardiac side. The cra¬nial side was ligated first. A polyethylene tube 1 mm,
o.d. and 0.1 mm, i.d. with its tip drawn to a tapered end (by stretching) serves as the venous cannula. To its outer end was attached a metal cannula (David Kopf intra cerebro ventricular cannula cat no. 201 or 220) with hollow-set screw and rubber diaphragm (Figure 1). The total dead space from the rubber dia¬phragm to the tip of the polyethylene cannula was less than 10 µl. It was filled with saline, introduced into the vein through a small nick and was securely fixed with ligatures. The mouse was placed on the slide and one ear was fixed flat with cello tape to the slide. It was now placed under the clips of the micro¬scope stage. The metal cannula can also be fixed with a cello tape to the stage of the microscope. Drugs were injected at will with Hamilton syringe by punc¬turing the rubber diaphragm of the cannula.
The arterioles, venules, capillaries with different ve¬locities of flow were clearly visualized in the gaps of the epithelial cells. The fast red cell flow in arterioles and venules and slow hesitant and sometimes re¬versed flow in communicating capillaries was ob¬served. The fields can be selected to study the veins, arterioles or capillaries under suitable magnification. Vasodilation and decrease in flow velocity with drugs having instant effect like acetylcholine can be read¬ily seen.

The breed of hairless mouse is not readily available. 2. The commonly available albino mouse with hair re¬moved by a depilatory cream can serve as substi¬tute in studies on microcirculation. Further the main 3. advantage of this method is that the mouse can be placed on a large standard glass slide held by spring clips to the microscope stage. Easy to and fro move¬ment of the stage with the slide helps to select a satisfactory field. The thin and transparent ear under the cello tape permits use of all objectives of micro-5. scope to study the microcirculation under trans-illu¬mination with suitable magnification. There is no trauma to the ear. The same animal can be used repeatedly for comparison. The set up with a cannu-6. lated jugular vein provides for visualization of instant effects of drugs on microcirculation. Light anesthesia keeps the mouse still without disturbing the study. This is a convenient set up for research or demon-7. stration of microcirculation. It permits projection on to a screen and video recording with suitable equip¬ment where facilities are available. We could not record for want of video recording or micro photo-8. graphic equipment which is a limitation of this study.
　

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Spinotrapezius muscle microcirculatory function: effects of surgical exteriorization

Intravital microscopy facilitates insights into muscle microcirculatory structural and functional control, provided that surgical exteriorization does not impact vascular function. We utilized a novel combination of phosphorescence quenching, microvascular oxygen pressure (microvascular PO2), and microsphere (blood flow) techniques to evaluate static and dynamic behavior within the exposed intact (I) and exteriorized (EX) rat spinotrapezius muscle. I and EX muscles were studied under control, metabolic blockade with 2,4-dinitrophenol (DNP), and electrically stimulated conditions with 1-Hz contractions, and across switches from 21 to 100% and 10% inspired O2. Surgical preparation did not alter spinotrapezius muscle blood flow in either I or EX muscle. DNP elevated muscle blood flow ~120% (P < 0.05) in both I and EX muscles (P > 0.05 between I and EX). Contractions reduced microvascular PO2 from 30.4 ± 4.3 to 21.8 ± 4.8 mmHg in I muscle and from 33.2 ± 3.0 to 25.9 ± 2.8 mmHg in EX muscles with no difference between I and EX. In each O2 condition, there was no difference (each P > 0.05) in microvascular PO2 between I and EX muscles (21% O2: I = 37 ± 1; EX = 36 ± 1; 100%: I = 62 ± 5; EX = 51 ± 9; 10%: I = 20 ± 1; EX = 17 ± 2 mmHg). Similarly, the dynamic behavior of microvascular PO2 to altered inspired O2 was unaffected by the EX procedure [half-time (t1/2) to 100% O2: I = 23 ± 5; EX = 23 ± 4; t1/2 to 10%: I = 14 ± 2; EX = 16 ± 2 s, both P > 0.05]. These results demonstrate that the spinotrapezius muscle can be EX without significant alteration of microvascular integrity and responsiveness under the conditions assessed.
THE VIABILITY OF SKELETAL MUSCLE depends on the presence of a functional microvascular bed that provides adequate supply of oxygen and nutrients to, and removal of waste products from, the tissue. Important insights into muscle microcirculatory function in health and disease have been achieved with the use of intravital microscopy techniques that necessitate surgical exteriorization of the muscle. In this regard, the rat spinotrapezius preparation first described by Gray in 1973 (9) represents one principal model in which to evaluate physiological and pathophysiological phenomena within the microcirculation. For example, the rat spinotrapezius has been pivotal in our understanding of the effects of muscle structure-function relationships and smooth muscle physiology (16, 19, 33) and the role of nitric oxide and calcium in the microcirculation in health (24, 41). In addition, the spinotrapezius muscle preparation has provided insights into the pathophysiological microcirculatory consequences of chronic diseases such as type-1 diabetes (14, 35), hypertension (30), and chronic heart failure (6, 15). The tacit assumption in all of those studies has been that surgical intervention does not impact microcirculatory function either under control conditions or in response to experimental or pathological stimuli. However, it has been demonstrated that arterial and arteriolar pressures are reduced in the cremaster muscle after an exteriorization procedure that interrupts the distal blood supply emanating from the deferential artery (5).
To evaluate the effect of muscle exteriorization on the functional integrity of the microcirculation, the experimental methodology employed must be suitable for evaluation of not only blood flow (O2 delivery) but also the balance between O2 delivery and utilization in both the intact and exteriorized preparations. Moreover, in addition to steady-state conditions, the dynamic response of the microcirculation should be evaluated. Consequently, a novel combination of phosphorescence quenching and microsphere techniques was utilized across a range of different experimental conditions, i.e., metabolic stimulation with 2,4-dinitrophenol (DNP), electrically stimulated muscle contractions, and inspired hypoxia and hyperoxia, designed to evaluate the effect of surgical intervention on integrated static and dynamic microcirculatory behaviors within the rat spinotrapezius muscle.

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http://ajpheart.physiology.org/cgi/content/full/279/6/H3131

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