Micropuncture studies were performed in three groups of euvolemic male Munich-Wistar rats: 8 control rats, 7 severely hyperglycemic rats made diabetic with streptozotocin (60 mg/kg, i.v.), and 6 moderately hyperglycemic rats made diabetic by the same method but given 2 U of NPH insulin daily. Glucose concentrations at the time of micropuncture study averaged 115 +/- (sem) 10, 565 +/- 12, and 375 +/- 23 mg/dl, respectively. Single nephron GFR (SNGFR) values were significantly lower (28.8 +/- 1.9nl/min) in severely hyperglycemic rats than they were in controls (48.9 +/- 3.8). This reduction in SNGFR was due mainly to a fall in glomerular plasma flow rate ((Q(A)). In contrast, moderately hyperglycemic rats exhibited glomerular hyperfiltration, with SNGFR values averaging 69.0 +/- 8.0 nl/min. This hyperfiltration, with resulted from elevations in values for Q(A) and glomerular transcapillary hydraulic pressure difference (delta P) to levels significantly above control. These alterations in SNGFR in severely hyperglycemic and moderately hyperglycemic rats, relative to controls, were paralleled by changes in whole kidney GFR and mimic the changes in GFR observed in diabetic patients with analogous degrees of hyperglycemia. Measurements of blood volumes in separate groups of control, severely, and moderately hyperglycemic rats revealed equivalent absolute blood volumes in all three conditions and increased blood volumes, relative to body weight, in both groups of hyperglycemic rats. Thus, SNGFR is increased in diabetic rats with moderate hyperglycemia but decreased in those with severe hyperglycemia, and these changes are not simply related to variations in circulating blood volume.

To determine the permselectivity characteristics of the glomerular capillary wall, known molecular size fractions of [3H]dextran, prepared by gel chromatography, were infused into normally hydrated Wistar rats, thus permitting simultaneous measurement of Bowman's space/plasma water (BS/P) and urine/plasma water (U/P) concentration ratios, along with glomerular pressures and flows. Since (BS/P)inulin = 1.01 +/- 0.01 SE(n = 34, radius = approximately 14 A) and since (BS/P)dextran/(BS/P)inulin equaled (U/P)dextran/(U/P)inulin for dextrans ranging in molecular radius from 21 to 35 A, these findings validate that dextrans are neither secreted nor reabsorbed. For dextran radii of 20, 24, 28, 32, 36, 40, and 44 A, (U/P)dextran/(U/P)inulin averaged 0.99, 0.92, 0.69, 0.42, 0.19, 0.06, and 0.01, respectively. In accord with theoretical predictions that these fractional dextran clearances should vary appreciably with changes in glomerular transcapillary pressures and flows, an increase in glomerular plasma flow rate, induced in these same rats by plasma volume expansion, resulted in a highly significant lowering of fractional clearance of all but the smallest and largest dextrans studied. These findings emphasize that fractional solute clearances alone are inadequate to describe the permselective properties of the glomerular capillary wall unless glomerular pressures and flows are also known. This sensitivity of fractional dextran clearance to changes in plasma flow indicates that dextrans are transported across the capillary not only by bulk flow but also to an important extent by diffusion.

A B ST R A CT Using a unique strain of \VNistar rats endowed with glomeruli situated directly on the renal cortical surface, we measured glomerular capillary pressures using servo-nulling micropipette transducer techniques. Pressures in 12 glomerular capillaries from 7 rats averaged 60 cm H20, or approximately 50% of mean systemic arterial values. Wave form characteristics for these glomerular capillaries were found to be remarkably similar to those of the central aorta. From similarly direct estimates of hydrostatic pressures in proximal tubules, and colloid osmotic pressures in systemic and efferent arteriolar plasmas, the net driving force for ultrafiltration was calculated. The average value of 14 cm H20 is lower by some two-thirds than the majority of estimates reported previously based on indirect techniques. Single nephron GFR (glomerular filtration rate) was also measured in these rats, thereby permitting calculation of the glomerular capillary ultrafiltration coefficient.

Renin-angiotensin blockade lowers MCP-1 expression in dia-to precede the earliest manifestations of diabetic betic rats.nephropathy [1][2][3]. In rats made diabetic with streptozo-Background. Glomerular macrophage accumulation in diatocin (STZ) and maintained at moderate levels of hyperbetes implicates monocyte recruitment mechanisms in the glycemia by daily insulin injections, glomerular hyperpathogenesis of diabetic nephropathy. To test the hypothesis filtration, caused by elevations of glomerular perfusion that overexpression of monocyte chemoattractant protein-1 (MCP-1), a monocyte chemoattractant, is attenuated by reninand intracapillary hydraulic pressure (glomerular capilangiotensin system (RAS) inhibition, we assessed expression lary hypertension), likewise presages glomerular injury of genes regulating monocyte transmigration in the glomeruli [4]. Both glomerular capillary hypertension and the subof diabetic rats. sequent development of glomerular injury are dependent Methods. Competitive reverse transcription-polymerase chain on an intact renin-angiotensin system (RAS), as revealed reaction (RT-PCR) was used to semiquantitate mRNA expression in glomeruli harvested by sieving at serial intervals after by earlier studies from this laboratory showing that treatthe induction of diabetes by streptozotocin in Munich-Wistar ment with angiotensin-converting enzyme inhibitors rats. Although subject to limitations, competitive RT-PCR pro-(ACEIs) [5], alleviated glomerular capillary hypertenvides an objective measure suited to the minute quantities of sion and prevented the development of diabetic ne-RNA extractable from glomerular isolates. Results. Time-dependent elevation of MCP-1 expression phropathy in STZ rats, independent of glycemic control. was dramatically suppressed by treatment with the angiotensin-These studies established the experimental basis for the converting enzyme inhibitor enalapril or the AT1 receptor antagfirst successful large-scale clinical trial of ACEI in type onist candesartan, and was closely associated with effects on I diabetic patients [6]. proteinuria and glomerular macrophage number. By contrast, Glomerular injury occurring in the context of angiono sustained suppression of the cell adhesion molecules intercellular adhesion molecule-1 or vascular cell adhesion moletensin-dependent processes, including augmented glocule-1 or the classic MCP-1 stimulators tumor necrosis factor-␣ merular hemodynamics, may involve mononuclear cells or interleukin-1␤ followed RAS inhibition, and suppression of and an array of cytokines and other proinflammatory transforming growth factor-␤1 expression was transient. molecules. Evidence is accumulating that supports theConclusion. These data suggest that glomerular macrophage recruitment in experimental diabetes is largely determined by hypothesis that macrophages and macrophage products angiotensin-stimulated MCP-1 expression. We conclude that play a significant role not only in inflammatory glomeruthe RAS is an important regulator of local MCP-1 expre...