Diabetic Vessel Research Articles

Analysis of risk factors in diabetic retinopathy and intervention status

Diabetic retinopathy is one of diabetic capillary vessel complications,its occurrence is most high in the diabetic ocular region complication.If not totreat in time,it would result in blindness.The patients'life quality would be improved greatly by active prevention and treatment.In this article,to analyze the risk factors of diabetic retlnopathy and put forward intervention measures. Key words: Diabetic retinopathy; Risk factors; Intervention

Matrix metalloproteinases: keys to healthier blood vessels in diabetes?

In this issue of Journal of Endocrinology, Schuyler et al. show that intimal lesions in atherosclerosis-prone diabetic apoE(-/-) mice are reduced by insulin treatment. An increase of metalloproteinase-9 expression was observed in untreated diabetic apoE(-/-) mice; this was absent in insulin-treated mice. The study suggests that hindering of tissue-remodeling metalloproteinases may account for the beneficial effects of proper metabolic control in patients with diabetes. This clinically relevant finding prompts further exploration.

Vascular protective effects of selective PKCb inhibitor with Ruboxistaurin in Murine models

Shi-Fang Yan New York University School of Medicine, USA A a growing body of evidence from animal and human studies indicates benefi cial eff ects of protein kinase C  (PKC) inhibition on microvascular parameters, our studies have examined the eff ects of PKC inhibitor, ruboxistaurin, on macrovascular disease in the experimental murine models of atherosclerosis, restenosis, myocardial ischemia, and lung ischemia. Wild type C57BL6 and apoE-/male mice were maintained on normal rodent chow and then fed normal chow containing the PKCβ inhibitor, ruboxistaurin (LY333531) or vehicle chow without inhibitor. Mice were rendered diabetic (D) (defi ned as plasma glucose >250 mg/ dl) by injection of streptozotocin (65μg/g weight) for fi ve consecutive days at age 6 weeks. Our data provide the fi rst evidence that key species and stresses implicated in vascular injury, such as modifi ed lipoproteins, glucose and diacylglycerol (DAG), acute physical stress, hypoxia and ischemia/reperfusion transduce their key pathogenic eff ects, at least in part, via rapid and, in certain settings, chronic recruitment of PKC signaling pathway. Th is work raises the possibility that blockade of the PKC by a pharmacologic inhibitor, ruboxistaurin, may attenuate neointimal expansion or organ dysfunction and damage triggered by acute mechanical injury, chronic atherosclerosis, or ischemia-reperfusion stress. In addition, based on the bioavailability and tolerability of ruboxistaurin in diabetes and our fi ndings in euglycemia and diabetic atherosclerosis, we speculate that blockade of PKC signaling pathway may hold promise as a therapeutic intervention in treating macrovascular disease involving the heart and large vessels in both diabetes and non-diabetes, although this remains to be proven in clinical trials.

Reduced Retinal Vessel Response to Flicker Stimulation but Not to Exogenous Nitric Oxide in Type 1 Diabetes

Various studies have shown that retinal vessels in patients with diabetes mellitus have a reduced capacity to adapt to changes in perfusion pressure and to stimulation with flickering light. Structural and functional changes in retinal vessels in diabetes could lead to a general reduction of vasodilator and/or vasoconstrictor capacity. To gain more insight into this topic, we compared the response of retinal vessel diameters to systemic glyceryl trinitrate (GTN) and stimulation with diffuse luminance flicker in patients with diabetes and healthy control subjects. Twenty patients with type 1 diabetes mellitus featuring no or mild nonproliferative diabetic retinopathy and 20 healthy, age-matched subjects were included in this study. A vessel analyzer was used for measurement of diameters of retinal arteries and veins. The response of diameters was measured continuously during stimulation with flickering light, as well as immediately after sublingual application of 0.8 mg GTN. The response of retinal vessels to flickering light was significantly reduced in the patients with diabetes (arteries: 2.9% in diabetes versus 7.0% in control subjects, P < 0.002; veins: 4.6% in diabetes versus 6.8% in control subjects, P = 0.020). GTN-induced vasodilatation was not different between the patients with diabetes and the healthy control subjects (P >or= 0.70). The present study confirmed reduced response of retinal vessels to stimulation with flickering light in diabetes. The response of retinal vessels to a direct NO-donor, however, was maintained. This result indicates that abnormal flicker-induced vasodilatation in diabetes is not a consequence of generally reduced retinal vascular reactivity (ClinicalTrials.gov number, NCT00432029).

No‐induced retinal vasodilatation is maintained in type 1 diabetes

Abstract Purpose Various studies have shown that retinal vessels in patients with diabetes mellitus have a reduced capacity to adapt to changes of perfusion pressure. The mechanisms lying behind this abnormal autoregulation have not been completely identified yet. Histomorphological changes of retinal vessels in diabetes could possibly reduce their capacity of vasodilation and vasoconstriction. To test this hypothesis we compared the response of retinal vessel diameters to systemic glyceryl trinitrate (GTN) in patients with diabetes and healthy controls. Methods 20 patients with insulin dependent diabetes mellitus featuring no or mild non‐proliferative diabetic retinopathy were included into this study. In addition, 20 healthy and age‐matched subjects were included as controls. Retinal vessel diameters were measured before and immediately after sublingual application of 0.8 mg of the NO‐donor GTN. The IMEDOS Retinal Vessel Analyzer was used for continuous measurement of diameters of retinal arteries and veins. Results Oral application of GTN induced vasodilatation of retinal arteries and veins. This effect was not different between patients with diabetes and healthy controls. Systemic arterial blood pressure was reduced in both groups after GTN application, but to a comparable degree. Conclusion The present study indicates that in patients with no or mild non‐proliferative diabetic retinopathy the vasodilatory response of retinal vessels to a direct NO‐donor is maintained. This indicates that abnormal retinal autoregulation in diabetes mellitus, as observed previously, is not a consequence of generally reduced retinal vascular reactivity.

The Role of AGEs in Cardiovascular Disease

Advanced glycation end-products (AGEs) are generated in the diabetic milieu, as a result of chronic hyperglycemia and enhanced oxidative stress. These AGEs, via direct and receptor dependent pathways promote the development and progression of cardiovascular disease. AGEs accumulate at many sites of the body including the heart and large blood vessels in diabetes. These modified proteins interact with receptors such as RAGE to induce oxidative stress, increase inflammation by promoting NFkappaB activation and enhance extracellular matrix accumulation. These biological effects translate to accelerated plaque formation in diabetes as well as increased cardiac fibrosis with consequent effects on cardiac function. Strategies to reduce the ligation of AGEs to their receptors such as agents which reduce AGE accumulation, soluble RAGE which acts as a competitive antagonist to the binding of AGEs to RAGE and genetic deletions of RAGE appear to attenuate diabetes associated atherosclerosis. Benefits on cardiac dysfunction with these inhibitors of the AGE/RAGE axis are not as well characterised. In conclusion, therapeutic strategies targeting AGEs appear to have significant clinical potential, often in combination with currently used agents such as inhibitors of the renin-angiotensin system, to reduce the major burden of diabetes, its associated cardiovascular complications.

Influence of Flickering Light on the Retinal Vessels in Diabetic Patients

Stimulation of the retina with flickering light increases retinal vessel diameters in humans. Nitric oxide is a mediator of the retinal vasodilation to flicker. The reduction of vasodilation is considered an endothelial dysfunction. We investigated the response of retinal vessels to flickering light in diabetic patients in different stages of diabetic retinopathy. We studied 53 healthy volunteers, 68 type 1 diabetic patients, and 172 type 2 diabetic patients. The diameter of retinal vessels was measured continuously online with the Dynamic Vessel Analyzer (DVA). Diabetic retinopathy was classified using Early Treatment Diabetic Retinopathy Study criteria. Changes in vasodilation are expressed as percent change over baseline values. After adjustments for age, sex, and antihypertensive treatment, the response of retinal arterioles to diffuse luminance flicker was significantly diminished in patients with type 1 diabetes compared with healthy volunteers. The vasodilation of retinal arterioles and venules decreased continuously with increasing stages of diabetic retinopathy. The retinal arterial diameter change was 3.6 +/- 2.1% in the control group, 2.6 +/- 2.5% in the no diabetic retinopathy group, 2.0 +/- 2.7% in the mild nonproliferative diabetic retinopathy (NPDR) group, 1.6 +/- 2.2% in the moderate NPDR group, 1.8 +/- 1.9% in severe NPDR group, and 0.8 +/- 1.6% in proliferative diabetic retinopathy group. Flicker responses of retinal vessels are abnormally reduced in diabetic patients. This decreased response deteriorated with increasing stages of retinopathy. The response was already reduced before clinical appearance of retinopathy. The noninvasive testing of retinal autoregulation with DVA might prove to be of value in early detection of diabetic vessel pathological changes.

Microvascular tissue plasminogen activator is reduced in diabetic neuropathy

Abnormalities of endogenous fibrinolysis are linked to diabetic macrovascular disease; whether key vascular endothelial regulatory proteins, such as tissue plasminogen activator (tPA), are altered in diabetic neuropathy microvasculature is unknown. This neuropathologic case: control study investigates the hypothesis that tPA expression is regionally deficient in microvessels in human diabetic neuropathy. tPA and von Willebrand factor (vWF), a vascular endothelial cell marker, are detected on vascular endothelium by immunoperoxidase methods with specific antibodies on formalin fixed paraffin embedded sural nerve biopsies from six diabetic and six axonal neuropathy control nerves without vasculopathy. The proportion of microvessels in each nerve region expressing tPA is determined by the ratio of tPA positive vessels/total vWF positive vessels on serial sections. tPA expression is lower in diabetic neuropathy cases compared to controls in all regions, including epineurial (62.4 +/- 8.6% vs 91.0 +/- 1.6%, p < 0.02) and endoneurial microvessels (51.7 +/- 7.1% vs 91.5 +/- 2.9%, p < 0.001). These results demonstrate a four- to sixfold increase in the number of peripheral nerve microvessels lacking immunodetectable tissue plasminogen activator in the epineurial and endoneurial vessels in diabetes, suggesting that impaired endogenous fibrinolysis might contribute to microvascular ischemia in human diabetic neuropathy.

Small Interfering RNA-mediated Caveolin-1 Knockout on Plasminogen Activator Inhibitor-1 Expression in Insulin-stimulated Human Vascular Endothelial Cells

Using human vascular endothelial cells (ECV304) as the target, we studied the effect of caveolin (CAV)-1 in the course of insulin-stimulated expression of plasminogen activator inhibitor (PAI)-1. The appropriate single-stranded oligonucleotides representing the RNAi CAV-1 gene were analyzed by Ambion software. After annealing to generate double-stranded oligonucleotides (ds oligo), it was cloned into the pENTR/U6 entry vector containing RNA polymerase III expression element by T4 DNA ligase. The short hairpin (shRNA) sequences transferred from the pENTR/U6 entry were cloned into the pLenti6/BLOCK-iT-DEST vector with an LR recombination reaction. After identification by sequencing, we successfully constructed the CAV-1 RNAi lentiviral expression system using Gateway technology. Silencing efficiency was assayed by real-time reverse transcription-polymerase chain reaction, immunofluorescence staining and Western blotting. ECV304 cells were cultured in the medium containing different concentrations of insulin (1x10(-9) to 1x10(-7) M) with the CAV-1 gene silenced or not. The expression level and subcellular localization of PAI-1 and CAV-1 were compared using reverse transcription-polymerase chain reaction, immunofluorescence staining and Western blot assay. The results showed that the potent inhibition of CAV-1 expression could reach 85%, and it was specific to the CAV-1-derived shRNA, not the S100A13-derived shRNA. There was no dramatic difference in PAI-1 expression between the RNAi+ and RNAi- ECV304 cells incubated with physiological insulin, but PAI-1 protein did accumulate under the cell membrane. As the concentration of insulin increased, the expression of PAI-1 was up-regulated, whereas the expression of CAV-1 attenuated. Furthermore, PAI-1 clearly augmented after CAV-1 knockdown. These results indicated that hyperinsulinism could promote PAI-1 expression by inhibiting CAV-1, and stabilizing or up-regulating CAV-1 expression in endothelial cells might reduce complications of the great vessels and capillary vessels in diabetes.

Sphingosine-1-Phosphate

See related article, pages 731–739 A key question in unlocking the mystery of accelerated atherosclerosis that often accompanies types1 and 2 diabetes and leads to increased incidence and severity of heart attacks and strokes is, what are the precise biochemical and molecular signaling pathways that perturb the diabetic blood vessel leading to acceleration of vascular inflammation and atherosclerosis? Extensive evidence implicates elevated levels of glucose as a critical culprit in these phenomena. Beyond a critical threshold, it is apparent that increased glucose levels significantly exceed homeostatic requirements, and divert fundamental pathways leading to untoward nonphysiological effects in the cells. Glucose may be dangerous, not solely because of its direct effects, but because of its long-term consequences. The studies of the Diabetes Control Clinical Trials (DCCT) and the Epidemiology of Diabetes Interventions and Complications Research (EDIC) Groups showed definitively that earlier rigorous glycemic control, despite eventual normalization of glucose levels compared with conventionally-treated type 1 diabetic subjects, exerted long-term protection against surrogate (carotid intima-media thickness) and frank end points (cardiovascular events and death) of cardiovascular disease.1–2 Why is the diabetic vessel so vulnerable to increased glucose? A plausible hypothesis is that it’s not just glucose; rather, excessive glucose is accompanied by clever accomplices in the pathways leading to irreversible vascular injury, some of which may be directly influenced by adverse signals emitted by hyperglycemia. For example, the nonenzymatic glycation and oxidation of proteins and lipids results in the generation of Advanced Glycation Endproducts (AGEs), key signaling species that perturb endothelium, smooth muscle cells and monocytes to ignite vascular inflammation and contribute to accelerated atherogenesis and the development and progression of vulnerable atherosclerotic plaques.3 AGEs, by virtue of their interaction with Receptor for AGE (RAGE), trigger generation of oxidative species and activation of downstream proinflammatory and prothrombotic pathways. Importantly, …

Blood Platelet Reactivity and its Pharmacological Modulation in (People with) Diabetes Mellitus

Blood platelets play a crucial role in physiological haemostasis and in pathology of prothrombotic states, including atherosclerosis. In this paper, we review major factors underlying altered platelet reactivity, with special attention paid to abnormalities in platelet function in people with diabetes mellitus (DM). The overall picture of platelet abnormalities in DM, including altered adhesion and aggregation, is hypersensitivity of diabetic platelets to agonists. "Primed" diabetic platelets respond more frequently even to subthreshold stimuli, sooner become exhausted, consumed and finally hyposensitive, thus contributing to accelerated thrombopoiesis and release of 'fresh' hyperreactive platelets. In diabetes disturbed carbohydrate and lipid metabolism may lead to physicochemical changes in cell membrane dynamics, and consequently result in altered exposure of surface membrane receptors. These phenomena, together with increased fibrinogen binding, prostanoid metabolism, phosphoinositide turnover and calcium mobilisation often present in diabetic patients, contribute to enhanced risk of small vessel occlusions and accelerated development of atherothrombotic disease of coronary, cerebral and other vessels in diabetes. As platelet hypersensitivity in DM makes a major contribution to enhanced risk of thromboembolic macroangiopathy, and consequently enhanced morbidity and mortality, it validates use of antiplatelet agents in diabetic individuals. Platelet hyperreactivity may be cured with various antiplatelet drugs to a considerably large extent notwithstanding, evidence gathered from clinical and experimental surveys shows that this approach may not always be equally efficient in people with diabetes. Observations from clinical studies rather support the use of multifactorial strategy under such circumstances, like a combined therapy of aspirin plus either purinoreceptor blocker or GPIIb-IIIa antagonist.

Angiopoietin-2-related modulation of retinal angiogenesis – A new model for diabetic retinopathy

Diabetic retinopathy is the most prevalent cause of blindness among adults of working age. The earlies discernible lesion in the diabetic retina is pericyte loss. The Angiopoietin-Tie system plays a central role in this process. We examined the impact of retinal Angiopoietin 2 (Ang-2) overexpression on capillary cell cross-talk. We established and characterized a transgenic mouse which expresses human Ang-2 under control of a murin opsin promoter. Physiological sprouting of postnatal retinal vessels was examined in lectin-stained retinal whole mount preparations. Quantitative morphometry of retinal digest preparations was used to assess the endothelial/pericyte ratio as a measure of changes in the cellular composition of capillaries. The effect of retinal Ang-2 overexpression on pathological neovascularization was studied in the mouse model of hypoxia-induced proliferative retinopathy. Physiological sprouting was accelerated by Ang-2 overexpression, in association with a 17% deficit of pericytes in the deep capillary layers. MOpsinHAng-2 mice had significantly more retinal neovascularizations, both within and outside the retina, compared with controls. Taken together, our data suggest that Ang-2 is involved in the interaction between pericytes and endothelial cells, and may play an important role in the response-to-injury of the diabetic vessel system.

AGE-related cross-linking of collagen is associated with aortic wall matrix stiffness in the pathogenesis of drug-induced diabetes in rats

Diabetes mellitus is major risk factor for cardiovascular disease, and atherosclerosis accounts for most of the morbidity and mortality of diabetic patients. To examine the effects of diabetes on the vessel wall, we examined the association of collagen cross-linking in relation to matrix stiffness of the descending aorta in streptozotocin-induced diabetic rats. The matrix stiffness of the vessel was determined by measuring the tensile properties of the tissue. Seven weeks following the establishment of diabetes, both control and diabetic rats were killed and the descending aortas were excised and analyzed. The findings from biomechanical analysis indicated a significant increase in maximum load (26%), stress (22%), Young's modulus of elasticity (60%), and toughness (32%) in diabetic aortas compared to control. In contrast, the maximum strain of the diabetic rat aorta was significantly reduced by 20% compared to control rats, suggesting stiffening of the blood vessel. The results from biochemical analysis showed that the amount of total collagen increased by 21% in diabetic tissues compared to the control. The sequential extractions of collagen showed that the diabetic specimens yielded 34% more neutral salt-soluble collagen (NSC) than the control. The amount of pepsin-soluble collagen was 31% less in diabetic tissues than in the control group, whereas the amount of insoluble collagen (ISC) increased by 56%. A significant accumulation in advanced glycation end products (AGEs) were seen in pepsin- and collagenase-soluble collagen in diabetic vessel. Furthermore, the altered biomechanical properties of the vessel wall were strongly correlated with the biochemistry of collagen. Overall, these results provide evidence that the diabetic state is associated with the changes in collagen biochemistry and in the biomechanics of the blood vessel.

Increased expression of thrombospondin-1 in vessel wall of diabetic Zucker rat.

Thrombospondin-1 (TSP-1) expression in the vascular wall has been related to the development of atherosclerotic lesions and restenosis. TSP-1 promotes the development of neointima and has recently been associated with atherogenesis at a genetic level. Because TSP-1 expression is responsive to glucose stimulation in mesangial cells, we hypothesized that glucose may stimulate its production by vascular cells. Thus, TSP-1 expression in the blood vessel wall may increase, providing a molecular link between diabetes and accelerated vascular lesion development. To determine whether the expression level of TSP-1 in vessel wall is increased in diabetes, aorta and carotid arteries of Zucker rats were used for immunostaining, Western blotting, and in situ RNA hybridization. A significant increase in TSP-1 expression was found in the adventitia of blood vessels from diabetic rats. Consistent with the well-known antiangiogenic effect of TSP-1, the number of vasa vasorum was reduced in aortas from diabetic rats. In cultured endothelial cells, vascular smooth muscle cells, and fibroblasts, TSP-1 expression increased in response to glucose stimulation (>30-fold). After balloon catheter injury to carotid arteries, expression of TSP-1 protein and mRNA was higher at all time points in the vessels of diabetic rats. Increased expression of TSP-1 in blood vessels in diabetes may represent a new link between diabetes, atherogenesis, and accelerated restenosis. This increase in TSP-1 production may be a direct response of vascular cells to glucose.

Gene therapy for renal disorders: what are the benefits for the elderly?

Chronic renal failure is one of the major health problems for the elderly. Currently, about 50% of all patients receiving chronic dialysis for end-stage renal disease (ESRD) are aged 65 years or older. Their first-year mortality rate is as high as 30%. The leading causes of ESRD in the elderly are diabetic nephropathy, hypertension and large vessel diseases, and glomerulonephritis. The elderly are also prone to developing acute renal failure induced by ischaemic injury or nephrotoxic drugs. Gene transfer in experimental animals have been tested in all of these conditions, as well as in animal kidney transplantation models, with various degrees of success. However, there are many obstacles to be overcome before gene therapy can be tested clinically for renal disorders. In particular, the major challenges include determining how to prolong and control transgene expression or antisense inhibition and how to minimise the adverse effects of viral or nonviral vectors. Once these problems are solved, gene therapy will have a role in treating age-related renal impairment.

Protein kinase C activation contributes to microvascular barrier dysfunction in the heart at early stages of diabetes.

The functional disturbance of microvasculature is recognized as an initiating mechanism that underlies the development of various diabetic complications. Although a causal relationship between microvascular leakage and tissue damage has been well documented in diabetic kidneys and eyes, there is a lack of information regarding the barrier function of coronary exchange vessels in the disease state. The aim of the present study was to evaluate the permeability property of coronary microvessels during the early development of experimental diabetes with a focus on the protein kinase C (PKC)-dependent signaling mechanism. The apparent permeability coefficient of albumin (Pa) was measured in isolated and perfused porcine coronary venules. The administration of high concentrations of D-glucose induced a dose-dependent increase in the Pa value, which was prevented by blockage of PKC with its selective inhibitors bisindolylmaleimide and Goe 6976. More importantly, an elevated basal permeability to albumin was observed in coronary venules at the early onset of streptozotocin-induced diabetes. The hyperpermeability was corrected with bisindolylmaleimide and the selective PKCbeta inhibitor hispidin. Concomitantly, protein kinase assay showed a high PKC activity in isolated diabetic venules. Immunoblot analysis of the diabetic heart revealed a significant subcellular translocation of PKCbetaII and PKCepsilon from the cytosol to the membrane, indicating that the specific activity of these isoforms was preferentially elevated. The results suggest that endothelial barrier dysfunction attributed to the activation of PKC occurs at the coronary exchange vessels in early diabetes.

Role of vascular basement membrane components in diabetic microangiopathy.

The complications of diabetic microangiopathy have been well documented clinically for many years; however, the specific cellular mechanisms that lead to the dysfunction of small vessels in diabetes are unknown. Histopathological studies on diabetic microangiopathy have established thickened vascular basement membrane as one of the first and foremost structural abnormalities. Evidence suggests that this fundamental structural lesion develops, at least in part, from excess accumulation of basement membrane material in the vessel walls. Several vascular basement membrane components have been identified whose expression is up-regulated in diabetes. Enzymes responsible for the degradation of basement membrane components have also been reported to exhibit reduced activity. Strategies are being developed to regulate the abnormal accumulation of extracellular matrix (ECM) components in diabetic microangiopathy. In experimental diabetes, aldose reductase inhibitors have been found to be effective in preventing vascular basement membrane thickening when applied soon after the onset of hyperhexosemia. Clinical trials have been initiated with inhibitors of protein kinase C, an enzyme that up-regulates the synthesis of ECM components in diabetes. Currently, gene therapy strategies are also being developed to inhibit specific gene expression responsible for excess ECM synthesis in diabetes. Recent studies in the authors' laboratory have shown the applicability and efficacy of antisense oligonucleotides toward reducing vascular basement membrane component synthesis. Several gene regulatory approaches are currently being developed to modulate and prevent vascular basement membrane component synthesis. Such strategies may help identify key events that underlie the complex developmental stages of diabetic microangiopathy.

Autoregulation of retinal arterioles in patients with diabetes mellitus and normal probands

Measurement of myogenic autoregulation of retinal arterioles was demonstrated by the use of the Retinal-Vessel-Analyzer (Carl Zeiss, Jena). The purpose of the presented study was to find a significant difference of this myogenic response in a group of healthy individuals vs. a group of patients with pathologic conditions. As a group of patients with known pathology in microcirculation patients with type 1 diabetes were chosen. By isometric exercise an identical rise in mean arterial blood-pressure was provoked in 20 patients with type-1 diabetes and 20 matched healthy volunteers. The myogenic response of retinal arterioles was measured in both groups by the use of the Retinal-Vessel-Analyzer. The Wilcoxon test was used for statistical analysis within the two groups whereas both groups were compared with each other by the use of the Mann-Whitney test. Having the same age and same blood-pressure rise (p = 0.624) a significant better myogenic response was found in the healthy subjects vs. the diabetic group (p = 0.008). In the diabetic group no correlation was found between myogenic response and duration of diabetes (p = 0.982) or HbA1c values (p = 0.83). In this study significant loss of autoregulation in patients with type 1 diabetes is demonstrated. By the use of the Retinal-Vessel-Analyzer noninvasive testing of the function of autoregulation of retinal arterioles is possible. This method might prove to be of great value in early detection of diabetic vessel pathology.

Ultrastructure and organization of the cutaneous microvasculature in normal and pathologic states.

The cutaneous microvasculature is organized into upper and lower horizontal plexuses with the dermal capillary loops arising from the upper plexus. The arteriolar and venular sides of the microvasculature can be identified by the ultrastructure of the mural basement membrane material. Collecting venules present in the lower dermis contain valves. Periadventitial cells (veil cells) are present around all microvessels. Their size and number appear to correlate with the quantity of mural basement membrane material found in cutaneous vessels in diabetes, actinic damage, and chronological aging. The contractile cells of the vascular wall surround the endothelial cell tube in a manner suggesting specific functions. The smooth muscle cells in the arteriolar segment form a sleeve, whereas each pericyte in the postcapillary venular simultaneously makes many contacts with several underlying endothelial cells. The common telangiectases can be explained by abnormalities in this organization and ultrastructure rather than by neovascularization or random anastomoses. The macular telangiectases seen in scleroderma, generalized essential telangiectasia, and nevus flammeus are produced by dilatation of the postcapillary venules of the upper horizontal plexus. Cherry angiomas are produced by spherical and tubular dilatations of capillary loops in dermal papillae with tortuous cross-connections between individual loops. Angiokeratomas of Fabry and Fordyce have the ultrastructure of collecting venules that contain valves, and appear to represent the ectopic development or placement of small valve-containing collecting veins. The cutaneous lesions of hereditary hemorrhagic telangiectasia represent arteriovenous communications.

Reduction of nerves containing vasoactive intestinal polypeptide and serotonin, but not neuropeptide Y and catecholamine, in cerebral blood vessels of the 8-week streptozotocin-induced diabetic rat.

The perivascular autonomic nerves of the major blood vessels on the ventral surface of the brain were studied in the streptozotocin-induced diabetic rat, an animal model for juvenile onset of diabetes. Histochemical and immunohistochemical techniques were used to determine the pattern and density of perivascular nerves containing catecholamine, 5-hydroxytryptamine (5-HT), vasoactive intestinal polypeptide (VIP) and neuropeptide Y (NPY). A significant reduction in the density and/or fluorescence intensity of 5-HT-immunoreactive nerves was observed in the circle of Willis and its main arterial branches namely: basilar, superior cerebellar, internal carotid, posterior communicating, middle cerebral and anterior cerebral arteries, while a significant reduction of VIP-immunoreactive nerves was observed in the internal carotid, middle cerebral and anterior cerebral arteries, but not in the basilar, superior cerebellar and posterior communicating arteries 8 weeks after the onset of diabetes. However, no changes were observed in the density of NPY- and catecholamine-containing nerves. The results are discussed in relation to autonomic neuropathy of the cerebral blood vessels in diabetes.