Alterations of the Rat Mesentery Vasculature in Experimental Diabetes

Abstract

SUMMARY:The alteration induced by diabetes on vascular permeability to serum albumin was investigated in the mesentery of streptozotocin-induced hyperglycemic rats. Double-tagged ( 125 I and dinitrophenol-haptenated) heterologous albumin was intravenously administered in normal and hyperglycemic animals, and the extravasation of the tracer was evaluated by radioactivity measurements and by morphometry at the ultrastructural level using quantitative protein A-colloidal gold immunocytochemistry. The results demonstrate that diabetes induces a significant increase in the permeability of the mesentery vessels to albumin. This increase is due to a more efficient transport of macromolecules by endothelial plasmalemmal vesicles and not to leakier interendothelial junctions. Passage across the endothelial basement membranes did not appear to be restricted in either the control or diabetic condition. However, in diabetes, the mesothelial basement membrane appeared to become modified and to restrain the passage of albumin toward the peritoneal cavity. After 3 months of diabetes, the rats presented a net increase in the average diameter of the blood vessels localized in the mesentery arcada (macrovascular hyperplasy) and a notable angiogenesis, manifested at the level of the microvasculature in the mesenteric windows. (Lab Invest 2000, 80:1171-1184.T he association of diabetes with vascular dysfunctions gradually evolving toward incapacitating or life-threatening vascular pathologies is undisputed. Extensive clinical observations and studies on animal models have amply documented that hyperglycemia accelerates and worsens atherosclerosis in large arteries (Colwell et al, 1988;Shantaram, 1999;Steiner 1997) and affects, although in different ways, the microvessels of selected vascular beds, such as those of the retina (Bazan et al, 1997;Cunha-Vaz, 1983;Porta, 1996;Ruggiero et al, 1997), kidney (Flyvbjerg, 1997;Mauer et al, 1984;Nyengaard and Bendtsen, 1993;Vlassara et al, 1994), and nerves (Cameron and Cotter, 1997;Malik et al, 1993; Tesfay et al, 1994). Particular attention has been directed to the study of diabetes-induced retinopathies and nephropathies, because of their obvious clinical implications. On the other hand, the impact of diabetes on other vascular beds has been generally overlooked. Therefore, it is not known whether diabetic microangiopathy concerns all blood vessels, creating a sort of "dysfunctional background" exacerbated in particular tissues by local factors to a full blown vascular pathology, or the vasculature of many organs is simply spared by the deleterious effects of hyperglycemia/ hypoinsulinemia. The latter hypothesis would fall in line with the ever-growing body of evidence pointing to important physiological and biochemical dissimilarities between various vascular segments (Boegehold, 1998;Rajotte et al, 1998;Thorin and Shreeve, 1998).Several morphologic features and physiologic parameters appear as leit motifs of diabetic microangiopathies. Among these, the thickening of the basement membran...

Morpho-functional studies of the blood-brain barrier in streptozotocin-induced diabetic rats

“…Similar increases in the total number of plasmalemmal vesicles was reported in endothelial cells of STZinjected animals at the level of the muscle capillaries [49]. Also a similar increase in albumin transport by endothelial cells was reported in mesenteric capillaries of hyperglycaemic animals [41]. The low number of the plasmalemmal vesicles in the CNS endothelial cells has been well established and is considered as one of the features responsible for the low permeability to macromolecules attributed to the blood-brain barrier [1,5,6,8,43].…”

“…The passage of this protein across the capillary wall was comparatively evaluated on brain frontal lobe tissues from age-matched normoglycaemic and STZ-injected rats at two intervals after the onset of the hyperglycaemic state. The relation between the density of the immunolabelling and the actual concentration of the detected tracer has been well established [41,42]. Changes in albumin permeability were found in normoglycaemic rats along with their age as well as between normo-glycaemic and hyperglycaemic rats.…”

“…Five of the 4-5 months hyperglycaemic rats, and their corresponding controls, received an intravenous injection of 2 ml of dinitrophenylated bovine serum albumin (DNP-BSA) (200 mg, during 1 to 2 min) in the jugular vein [40,41]. Prior to this, 2 ml of blood was retrieved with a heparinised syringe.…”

“…This approach has been applied successfully to show circulating proteins within vascular beds at steady state conditions or during perfusion experiments allowing for the delineation of transendothelial transport pathways across the vascular walls in control as well as in experimental and pathological conditions [14,38,39,40,41,42,43,44]. We thus investigated the distribution of endogenous albumin over the blood capillary wall of the CNS, as well as the dynamics of the exogenous albumin passage across the same capillary bed, both under control and diabetic conditions.…”

Advances in small animal mesentery models for in vivo flow cytometry, dynamic microscopy, and drug screening

“…In particular, this model was used in the first study of the effects of nitric oxide (NO) on lymph microvessels in vivo: Shirasawa et al [35] showed the influence of a NO synthase inhibitor on lymphatic diameter and contractile activity, which was reversed after applying an endogenous NO donor (L-arginine). This model has also been employed to study microcirculation disturbances in experimental models of diseases such as diabetes, ischemia, hemorrhage, shock, inflammation, tumor, edema, and others [2,4,13,21,22,36,37] . Recent discoveries in cell biology (e.g., identification of the genes, such as VEGF-C and VEGF-D, expressed by endothelium or endothelial g rowth factors for lymphatics), along with advances in optical techniques (e.g., lasers, high-speed digital cameras, powerful software) have increased interest in this model and its capabilities for studying the fundamentals of blood and lymph microcirculation, including its potential for the molecular imaging of individual cells in vivo [38][39][40] .…”