The kidney in diabetes

The kidneys as a target organ for secondary microvascular complications of diabetes mellitus represents a health problem of enormous social cost. Recent studies in man and animals strongly support the concept that the primary responsibility for diabetic nephropathy rests with the metabolic derangements of the diabetic state. However, these metabolic derangements have complex biological effects; it is unlikely that hyperglycemia, per se, produces all of the nephropathic influences of diabetes. Alterations in microvascular hemodynamics in diabetes probably contribute to glomerular pathology. These alterations may be based upon disturbed vasoactive control mechanisms regulating angiotensin and prostaglandin secretion and metabolism. Although much remains to be learned about the pathogenesis of glomerular basement membrane and mesangial thickening in diabetes, these central structural abnormalities appear separable. Mesangial thickening is reversible by cure of the diabetic state in rats whereas glomerular basement membrane thickening is not. Treatment for the diabetic patient with end-stage renal failure has recently improved markedly. Although presently, kidney transplants from living related donors appear best, cadaver transplants and long-term hemodialysis are reasonable options.     

Alterations of glomerular basement membrane charge and structure in diabetic nephropathy

Summary We examined glomerular basement membrane anionic site distribution identified by cationic gold in seven patients with insulin-dependent and four patients with non-insulin-dependent diabetes mellitus, presenting a spectrum of clinical and glomerular changes. Anionic sites were investigated by pretreatment of tissue with glycosaminoglycan-degrading enzymes prior to cationic gold staining. The distribution of chondroitin sulphate proteoglycans — a previously unrecognized glomerular basement membrane component — and type IV collagen was examined by immunoelectron microscopy to identify structural changes in the basement membrane. Findings were compared with those of non-diabetic patients showing minor proteinuria and morphologically normal glomerular basement membranes. Two patients, originally diagnosed as having diabetic nephropathy were also examined at 19 weeks and 5 years after renal transplantation. Characteristic redistribution of type IV collagen and chondroitin sulphate proteoglycans was noted in thickened glomerular basement membrane segments (>400 nm) of diabetic patients and those with renal transplants. Extension of anionic sites deep into the glomerular basement membrane at pH 2.5, together with loss of interna sites at pH 5.8 is unique to diabetic nephropathy. Reduced charge density was apparent in some patients due to thickening of the glomerular basement membrane, although the number of anionic sites per unit length of membrane was actually increased. Thus, charge aberration in diabetic nephropathy is due to displacement rather than loss of anionic sites. Removal of more than 90% of these sites by heparitinase, confirms their association with heparan sulphate proteoglycans. Similar derangement of anionic sites in all patients with diabetic nephropathy irrespective of the degree of proteinuria, suggests that a heparan sulphate proteoglycan-related charge barrier plays a minor role in controlling permeability of the diabetic glomerular basement membrane.Abbreviations BSA Bovine serum albumin - CG cationic gold - CSPG chondroitin sulphate proteoglycans - GAG glycosaminoglycan - GBM glomerular basement membrane - HSPG heparan sulphate proteoglycans - LRE lamina rara externa - LRI lamina rara interna - PCI protein:creatinine index     

Sorbinil does not prevent galactose-induced glomerular capillary basement membrane thickening in the rat

Summary We investigated the role of the polyol pathway in the pathogenesis of glomerular basement membrane thickening in galactosaemic rats, an animal model that develops basement membrane lesions comparable to those of human diabetic subjects. Normotensive Wistar-Kyoto rats fed a 30% galactose diet for nine months developed significant glomerular basement membrane thickening by comparison with rats on a control test diet (p=0.008). However, addition of an aldose reductase inhibitor, sorbinil (250 mg/kg diet), to the galactose diet did not prevent the increase in glomerular basement membrane thickness. Furthermore, by using a quantitative electron microscopic immunogold technique, we examined biochemical alterations in the composition of glomerular basement membranes in this animal model. The labelling density (comparable to relative concentration) of collagen type IV in thickened glomerular basement membranes of galactosaemic animals was significantly increased by comparison to those of control rats (p=0.015). However, there was no significant difference in labelling densities of laminin and heparan sulfate proteoglycan core protein of these animals. Thus, our results indicate that an increase in glomerular basement membrane thickness accompanied by an increase in the labelling density of collagen type IV occurs in the galactosaemic rats, but this thickening is not prevented by sorbinil at the dose used in this experiment. Our study raises the strong possibility that glomerular basement membrane thickening in galactosaemic rats may not be due to excessive polyol pathway activity.     

Circulating glycated albumin and glomerular anionic charges

Aiming to discern the mechanisms by which circulating glycated albumin alters the glomerular filtration properties that lead to glomerular dysfunction in diabetes, the authors studied the distribution and densities of anionic charges through the rat glomerular wall upon intravascular infusion of Amadori products, as well as in various conditions of increased glomerular permselectivity. Polylysine-gold was used as the probe to reveal the anionic charges. The study was carried on renal tissue sections of bovine serum albumin (BSA)- and glycated BSA-injected, normoglycemic animals. Results were generated through morphometrical evaluations of the gold labeling. Changes in glomerular anionic distribution were corroborated on renal tissue sections of short- and long-term diabetic rats and of normal newborn rats, situations known for abnormal glomerular filtration. Altered renal function in these conditions was clearly associated with changes in glomerular anionic charges. On the other hand, the infusion of glycated albumin in the circulation of normal rats, though altering glomerular filtration properties, did not modify the distribution and density of the polylysine-gold labeling through the glomerular basement membrane. Thus, anionic charges seem not to be the factor involved in the early changes of glomerular permeability induced by circulating glycated albumin.     

Effect of a low protein diet on the relationship of nonenzymatic glycation to altered renal structure and function in diabetes mellitus

Renal functional parameters including creatinine clearance, urinary albumin excretion, basement membrane thickening, and levels of nonenzymatic glycation of glomerular basement membrane were studied in streptozotocin-induced diabetic rats and age-matched controls subjected to low protein diet. In addition, these parameters were also assessed in diabetic and streptozotocin injected nondiabetic animals fed a 24% protein diet, which served as “positive controls.” While diabetic animals from both diet groups had similar elevated glycated hemoglobin levels and increased levels of nonenzymatic glycation of glomerular basement membrane, these were significantly elevated as compared to insulin treated diabetic (euglycemic), age-matched controls on an 8% protein diet, and streptozotocin injected nondiabetic animals from both diet groups. However, urinary albumin excretion and creatinine clearance levels were significantly elevated only in the 24% protein diet fed diabetics over values seen in the various groups of animals on 8% and controls on 24% protein diet. In contrast, there were no statistical differences among diabetic, euglycemic and control (8% and 24% protein) animals with respect to creatinine clearance, urinary albumin excretion, and glomerular basement membrane thickness. Taken together these data cast some doubt on the role of nonenzymatic glycation in the development of diabetic nephropathy. Moreover, hyperglycemia per se causes a compensatory increase in kidney size irrespective of protein intake; a low protein diet, however, inhibits the hyperfiltration commonly seen in early diabetic nephropathy. The authors, thus, hypothesize that a low protein diet, by preventing compensatory increase in blood flow to surviving nephrons, in some fashion protects these functional units from subsequent damage and possibly delays the onset of renal failure.     

The long-term effect of pancreatic islet allotransplantation on glomerular basement membrane thickening in experimental diabetes

Pancreatic islet cells were intraportally allotransplanted into rats 2 weeks after the induction of diabetes mellitus by streptozotocin. The effect of successful transplantation on glomerular basement membrane thickening was examined 14 months later. Four groups of animals were available for study; rats with accepted pancreatic islet transplants, rats in whom graft rejection was induced, diabetic non-transplanted rats, and age-matched normal controls. Animals with accepted grafts showed no significant basement membrane thickening when compared with age-matched normal controls, while animals with rejected grafts and nontransplanted diabetic animals showed significant glomerular basement membrane thickening compared with the other groups but were not significantly different from each other. The ability of early intraportal pancreatic islet cell allotransplantation to prevent glomerular basement membrane thickening indicates that the glycemic control achieved by this approach is superior to glycemic control by traditional insulin therapy. The results of this study confirm that early pancreatic islet allotransplantation can prevent the development of glomerular basement membrane thickening in diabetic recipient rats.     

The choriocapillaris in spontaneously diabetic rats.

During diabetes in rats, the choroid of the eye shows increased permeability to albumin, basement membrane thickening, and decreased anionic charge sites on the abluminal surfaces of the choriocapillary microvessels. In other microvascular beds, permeability differences are correlated with differences in luminal membrane microdomains as indicated by the distribution of luminal membrane anionic charge. To see whether luminal surface charge distribution or other structural features of the choroidal microvasculature become altered during diabetes, we studied spontaneously diabetic and control rats using ultrastructural tracers and morphometric techniques. Rats were injected with horseradish peroxidase and perfused with aldehydes, and then retina-choroid tissue sections were incubated with cationized ferritin, reacted to visualize peroxidase, and prepared for electron microscopic study. The most striking alterations in the diabetic rats were vascular debris and migrating cells resembling vascular cells in the choriocapillaris stroma, suggesting an increase in capillary turnover. In addition, extracellular matrix material was increased, and peroxidase uptake and ferritin binding were low in some vessels of the diabetic rats compared with the controls. Variability was large in the diabetic animals, however, and other vessels remained apparently normal.     

Localization of Fibril/Microfibril and Basement Membrane Collagens in Diabetic Glomerulosclerosis in Type 2 Diabetes

Collagen is one of the major components of the extracellular matrices of the kidney. Basement membrane collagen, type IV collagen, is the major component in normal glomeruli. Fibril and interstitial collagen such as type III collagen, type V collagen, and type VI collagen are minor components of glomerular extracellular matrices and are localized mainly in the interstitium. Diabetic glomerulosclerosis is characterized by the expansion of the glomerular mesangial matrix as well as by thickening of the glomerular basement membrane. In order to clarify the roles of these various types of collagen in the development of diabetic glomerulosclerosis, immunohistochemical studies were perfomed in kidney specimens from patients with Type 2 diabetes. Early glomerulosclerosis is characterized by expansion of mesangial matrix with basement membrane collagen. However, in later stages glomerulosclerosis is characterized by an increase in the minor collagen components, such as type V and type VI collagen or collagens not normally present, such as type III collagen. Mesangial cells are known to synthesize all these types of collagen. In diabetes, phenotypic change in mesangial cells might produce excess amounts of fibril and interstitial collagen such as type III, type V, and type VI collagen, thus, leading to glomerulosclerosis.     

Selective proteinuria in diabetic nephropathy in the rat is associated with a relative decrease in glomerular basement membrane heparan sulphate

Summary In the present study we investigated whether glomerular hyperfiltration and albuminuria in streptozotocin-induced diabetic nephropathy in male Wistar-Münich rats are associated with changes in the heparan sulphate content of the glomerular basement membrane. Rats with a diabetes mellitus duration of 8 months, treated with low doses of insulin, showed a significant increase in glomerular filtration rate (p<0.01) and effective renal plasma flow (p<0.05), without alterations in filtration fraction or mean arterial blood pressure. Diabetic rats developed progressive albuminuria (at 7 months, diabetic rats (D): 42±13 vs control rats (C): 0.5±0.2 mg/ 24 h, p<0.002) and a decrease of the selectivity index (clearance IgG/clearance albumin) of the proteinuria (at 7 months, D: 0.20±0.04 vs C: 0.39±0.17, p<0.05), suggesting loss of glomerular basement membrane charge. Light- and electron microscopy demonstrated a moderate increase of mesangial matrix and thickening of the glomerular basement membrane in the diabetic rats. Immunohistochemically an increase of laminin, collagen III and IV staining was observed in the mesangium and in the glomerular basement membrane, without alterations in glomerular basement membrane staining of heparan sulphate proteoglycan core protein or heparan sulphate. Giomerular basement membrane heparan sulphate content, quantitated in individual glomerular extracts by a new inhibition ELISA using a specific anti-glomerular basement membrane heparan sulphate monoclonal antibody (JM403), was not altered (median (range) D: 314 (152–941) vs C: 262 (244–467) ng heparan sulphate/mg glomerulus). However, the amount of glomerular 4-hydroxyproline, as a measure for collagen content, was significantly increased (D: 1665 (712–2014) vs C: 672 (515–1208) ng/mg glomerulus, p<0.01). Consequently, a significant decrease of the heparan sulphate/4-hydroxyproline ratio (D: 0.21 (0.14–1.16) vs C: 0.39 (0.30–0.47), p<0.05) was found. In summary, we demonstrate that in streptozotocin-diabetic rats glomerular hyperfiltration and a progressive, selective proteinuria are associated with a relative decrease of glomerular basement membrane heparan sulphate. Functionally, a diminished heparan sulphate-associated charge density within the glomerular basement membrane might explain the selective proteinuria in the diabetic rats.Abbreviations BW Body weight - ERPF effective renal plasma flow - GAG glycosaminoglycan - GBM glomerular basement membrane - GFR glomerular filtration rate - HS heparan sulphate - HSPG heparan sulphate proteoglycan - IDDM insulin-dependent diabetes mellitus - STZ streptozotocin     

Interactions between hypertension and diabetes on vascular function and structure in rats.

Regional 125I-albumin permeation and glomerular structural changes were assessed in male Sprague-Dawley rats with diabetes and/or hypertension. All rats underwent unilateral nephrectomy 2 weeks after induction of diabetes with streptozotocin. At the same time, one-half of the nondiabetic and diabetic animals were placed on 1% saline drinking water and given weekly intramuscular injections of deoxycorticosterone acetate to induce hypertension (systolic blood pressure greater than 150 mm Hg). Vascular permeability studies were performed after 1 and 3 months of hypertension. Hypertension, alone or in combination with diabetes, had no effect on weight gain, plasma glucose, or food consumption, but did increase 24-h urine volume in nondiabetics. In normotensive diabetics and in nondiabetic hypertensive rats, vascular 125I-albumin permeation was increased in eyes, aorta, and new granulation tissue (formed in a subcutaneous fabric implant), and glomerular basement membranes were thickened without any change in the fractional volume of the glomerulus occupied by mesangium. Urinary albumin and IgG excretion in nondiabetic hypertensive rats was increased much more than in normotensive diabetics. Hypertension and diabetes were additive in their effects on 125I-albumin permeation in eyes, aorta, and granulation tissue, and on glomerular basement membrane thickening, but were synergistic in their effects on urinary albumin excretion and mesangial fractional volume. The magnitude of the increase in vascular albumin permeation and urinary albumin and IgG excretion between and 1 and 3 months was much larger in diabetic hypertensive rats than in rats with hypertension or diabetes alone. Neither diabetes nor hypertension, alone or in combination, had any effect on albumin permeation in skeletal muscle, skin, heart, or brain. These findings demonstrate that hypertension and diabetes increase vascular albumin permeation in rats preferentially in tissues that correspond to sites of clinically significant vascular disease in human diabetics. They also attest to an important interaction between blood pressure-induced and diabetes-induced increases in vascular permeability in these tissues and in structural changes in the glomerular vasculature.     

Glomerular basement membrane changes in aging nondiabetic and diabetic guinea pigs

Glomerular hyperplasia and thickening or the glomerular basement membrane increase with age in humans and animals. This glomerulopathy can be enhanced by hyperglycemic conditions such as diabetes mellitus. When diabetic guinea pigs were examined by fluorescent microscopy, deposits of a substance similar to immunoglobulin G (IgG) were seen. Comparison with nondiabetic age-matched control animals suggest that glomerulopathy is related to aging, and can be further enhanced by hyperglycemia.     

The effects of aminoguanidine on renal changes in a baboon model of Type 1 diabetes

BACKGROUND: The efficacy of aminoguanidine (AG) on primary prevention of diabetic nephropathy was investigated in a nonhuman primate model of Type 1 diabetes over a period of 4 years. METHODS: Adolescent male baboons (Papio hamadryas) were assigned to four groups: control, diabetic, and control and diabetic treated with AG. Diabetes was induced with streptozocin (60 mg/kg) and treated with insulin to maintain a mean HbA1c level of about 9%. AG was given subcutaneously (10 mg/kg) each day. All animals had annual renal biopsies and 24-h urine collections for measurements of glomerular basement membrane (GBM) thickness, fractional mesangium volume (FMV), albumin excretion rate (AER), and creatinine clearance. Glomerular filtration rate (GFR) and renal plasma flow (RPF) were also determined. RESULT: The diabetic animals had increased GBM after 2 years of diabetes, but there was no increase in FMV over the study period. AG prevented the thickening of GBM at the 3- and 4-year time points. AG and diabetes synergistically increased the GFR. All diabetic animals developed increased albuminuria during the study although lower than the conventionally accepted microalbuminuria range. AG was not able to prevent this and, in fact, led to the nondiabetic animals also developing albuminuria. CONCLUSION: This is the first study to investigate the early use of AG in ameliorating renal damage in a primate model of Type 1 diabetes. The structural and functional changes in the kidney of these animals resemble those seen in the early stages of the human disease. AG was able to significantly reduce the thickening of GBM due to diabetes. This may suggest a potential role for this in primary prevention of diabetic nephropathy in the future.     

Urinary excretions of albumin and type IV collagen in normotensive and hypertensive subjects.

Plasma albumin leaks into urine as a result of glomerular hypertension and basement membrane injury, while urinary type IV collagen derives from mesangial matrix and glomerular basement membrane. The purpose of this study was to elucidate the pathophysiological significance of these urinary microproteins as an indicator of cardiovascular organ injuries in hypertension. In health-checkup participants without diabetes, proteinuria, or microhematuria, and who were not being treated for hypertension or any other disease at the time of enrollment, urinary albumin and type IV collagen were measured and their relations to organ injuries and cardiovascular risk factors were evaluated. Of 1,079 subjects (40- to 65-year-old; 256 men and 823 women) enrolled in the study, 120 (11.1%) had untreated hypertension exceeding 140/90 mmHg. Urinary albumin was positively correlated with both age (r=0.16, p<0.001) and systolic blood pressure (r=0.27, p<0.001). Urinary type IV collagen was not only positively correlated with age (r=0.12, p<0.001) and diastolic blood pressure (r=0.14, p<0.001) but also negatively correlated with blood hemoglobin (r=-0.12, p<0.001). Urinary albumin, but not type IV collagen, had a significant relation to electrocardiographic signs of left ventricular hypertrophy (p=0.012) and retinal arteriosclerosis on fundoscopy (p <0.001). Thus both albumin and type IV collagen would seem to have increased in association with age and hypertension in this cohort. It is suggested that urinary albumin is an indicator not only of renal injury, but also possibly of development of cardiac hypertrophy and arteriosclerotic changes. Urinary type IV collagen, on the other hand, may be associated with renal tissue injuries that affect erythrokinetics.     

Metabolic and ultrastructural aspects of experimental diabetic glomerulopathy

The effects of alloxan induced diabetes and insulin treatment on rat kidney glomerular ion transport and the oxidative phosphorylation were investigated in order to correlate metabolic and ultrastructural alterations. In alloxan diabetic rats an early decrease of Na+K+ ATPase activity in isolated glomeruli preparations and the subsequent uncoupling of oxidative phosphorylation were observed. These metabolic alterations are associated with structural changes such as the thickening of the basement membrane and the disorganization of both endothelial and mesangial cells. Insulin treatment induces a slow and only partial recovery of metabolic changes. Ultrastructural features of the kidney cortex were almost completely normalized after only two months of insulin treatment.     

Immunogold studies of monomeric elements from the globular domain (NC1) of type IV collagen in renal basement membranes during experimental diabetes in the rat

Summary The protein A-gold immunocytochemical technique was applied to reveal the monomeric elements M1, M2^* and M3 from the non-collagenous globular domain (NC1) of type IV collagen over various renal basement membranes from control and long-term streptozotocin-induced diabetic rats. This study includes the basement membranes of the proximal tubule, the Bowman's capsule and the glomerulus as well as the extracellular matrix of the mesangium. The labellings obtained were confined to basement membrane material. The quantitative analysis demonstrated changes in labelling intensities and distribution between tissues from normal and diabetic animals. Increased labelling intensities were observed for M1 and M2^* monomers in all the basement membranes studied except for the mesangial matrix which remained unchanged. In addition, the labelling for M1 monomers, present on the endothelial side of the glomerular basement membrane of control animals, was found to be distributed throughout the entire thickness of the basement membrane of diabetic animals. In contrast, neither the intensity of the labelling, nor the distribution of M3 monomers were altered in diabetic animals. Since M1 monomers are markers of the 1(IV) and 2(IV) chains of type IV collagen while M2^* and M3 mark 3(IV) and 4(IV) chains respectively, the present results demonstrate changes in the nature of the collagenous elements of basement membranes during diabetes. Furthermore, the results indicate that the 3(IV) and the 4(IV) chains are not necessarily present in the same molecule. The modifications of the collagenous elements of the basement membranes during diabetes must alter the structural characteristics of these matrices which in turn might influence their functional properties.     

The glomerular endothelium and the development of diabetic glomerulosclerosis

Summary Kidney ultrastructure was examined in biopsies obtained from 12 in-patients (7 females and 5 males) aged 6 to 18 with diabetes of 2 to 8 years’ standing. Special attention was focussed on the glomerular endothelium. The findings were suggestive of increased permeability of the glomerular endothelium with subsequent accumulation of ‘plasma-like’ material between the endothelial layer and the basement membrane. Other aspects are suggestive of the infiltration of the accumulated material towards the mesangial area, and its condensation which leads to the aspects usually interpreted as basement membrane thickening and mesangial matrix proliferation. The implications of these findings are discussed and their possible role in the development of diabetic glomerulosclerosis is pointed out. According to the authors’ point of view the first glomerular alteration in diabetics is a functional disturbance of the glomerular endothelium leading gradually to the well-known basement membrane thickening and mesangial changes. The authors illustrate their hypothesis in a diagram. Traduzione a cura di G. U.     

Slowly Progressive Male Alport Syndrome Evaluated by Serial Biopsy: Importance of Type IV Collagen Staining

A slowly progressive middle-aged man initially diagnosed with thin basement membrane nephropathy based on extensive thinning of the glomerular basement membrane (GBM) was subsequently diagnosed with Alport syndrome (AS) by a serial renal biopsy eight years later. The ultrastructural analysis of the second biopsy indicated thickening and wrinkling with mild reticulation in the GBM, consistent with AS. However, a retrospective analysis of the first biopsy revealed mild attenuation of type IV collagen α5 chain staining, suggesting a potential diagnosis of AS, despite the lack of ultrastructural features of AS. We herein report the clinical usefulness of type IV collagen staining in the early diagnosis of AS.     

Electron microscopy of renal and ocular changes in virus-induced diabetes mellitus in mice

The eyes, kidneys and pancreas of mice (SJL/J) infected with encephalomyocarditis virus were examined by light and electron microscopy. Diabetic mice with the longest duration (6 months) of diabetes showed marked renal and ocular alterations. Fasting blood glucose levels were 17.8-21.9 mmol/l and glycosuria was present. Clinically, based on ophthalmoscopy and fluorescein angiography, retinal vessels were normal. Histologically, moderately decreased numbers of pericytes were noted following trypsin digestion. The basement membrane of inner retinal vessels showed significant thickening in diabetic mice. Corneal epithelial oedema was present and surface microvillus projections were decreased compared with control mice. The kidneys of the same animals showed nodular and diffuse glomerulosclerosis and mesangial thickening. Electron microscopy showed excessive accumulation of basement membrane-like material in the mesangium and the peripheral glomerular region. Histologically, moderate to advanced kidney disease was associated with relatively early retinopathy.     

Pathogenesis of diabetic glomerulopathy: hemodynamic considerations

Early stages of diabetes mellitus are characterized by glomerular hyperfiltration in humans and experimental animals. In diabetic rats, single nephron hyperfiltration results from elevations in the glomerular capillary plasma flow rate and hydraulic pressure, which are in turn associated with progressive albuminuria and morphologic injury. Interventions that ameliorate these hemodynamic adaptations afford protection against structural injury. Dietary protein restriction, which lowers glomerular filtration, perfusion, and hydraulic pressure, retards glomerular injury and limits capillary basement membrane thickening in both the glomerular and retinal circulatory beds. Alternatively, selective control of glomerular capillary hypertension using angiotensin I converting enzyme inhibitor therapy limits glomerular injury in this model as well. Each of these interventions is effective even in the absence of improved metabolic control, implying that hemodynamic factors per se are important in this pathogenic process. The pathophysiologic mechanisms of diabetic hyperfiltration remain incompletely elucidated. Recent studies invoke a potential role for atrial natriuretic peptide (ANP). Strict metabolic control abolishes the elevations of glomerular filtration rate and of plasma ANP levels in moderately hyperglycemic diabetic rats. Moreover, infusion of a specific ANP antibody reverses hyperfiltration in diabetic rats. Thus, hyperglycemia-induced chronic volume expansion may trigger ANP release, which in turn contributes to diabetic hyperfiltration. Hemodynamic factors may play an important role in the pathogenesis of extrarenal microangiopathy as well. Elevated peripheral capillary blood flows and/or hydraulic pressure may be found in many peripheral capillaries, in association with thickening of the capillary basement membrane. Dietary protein restriction, which lowers blood flow to many organs, limits retinal as well as glomerular basement membrane thickening in diabetic rats, suggesting that hemodynamically mediated structural injury is a diffuse phenomenon in the diabetic state.