In aggregate, the data support a major role for complement in PMN recruitment in this model and point to complement-independent mechanisms of proteinuria in antibody-mediated glomerulonephritis. These 'knockout' mice should prove valuable for defining the complement-activated mediator systems that regulate leukocyte recruitment and tissue injury in renal diseases.

The effect of molecular charge of proteins on proximal tubular reabsorption was evaluated in the rat. Native and two cationized forms of albumin, native and anionized lysozyme, and native and anionized cytochrome c were iodinated with 125I. The different forms of each type of protein were alternately microinfused into the same site of proximal convoluted tubules in vivo. Tubular reabsorption was determined as the difference between the amounts of TCA-precipitable radioactivity infused and recovered in the urine. At low concentration of albumin 5 times more cationized than anionic albumin and 2.7 times more cationic than anionized lysozyme were reabsorbed by the proximal tubule. At two of four concentrations, proximal tubular uptake of cationic cytochrome c exceeded that of anionized cytochrome c. Uptake of cationic cytochrome c exceeded that of cationic lysozyme; however, the difference in uptake between native cationic and anionized species of the two proteins was much greater for lysozyme than for cytochrome c. The data reveal that a higher isoelectric point significantly enhances proximal tubular reabsorption of albumin, lysozyme, and cytochrome c and that proteins with similar molecular weight and isoelectric point are not necessarily reabsorbed to the same degree. This suggests that in addition to total molecular charge the molecular configuration and/or distribution of electrical charges on teh protein surface determine protein binding by the luminal membrane and subsequent endocytosis by the proximal tubule.

We studied the hemodynamic response of the isolated erythrocyte-perfused kidney to 25 min of ischemia and found that renal vascular resistance (RVR) was increased in the reflow period (16.7 +/- 1.4 mmHg.ml-1.min.g following ischemia vs. 10.2 +/- 0.8 mmHg.ml-1.min.g in control kidneys). Endothelial independent vasodilators [atrial natriuretic factor (ANF) and sodium nitroprusside] prevented the increase in RVR that occurred after ischemia. In contrast, acetylcholine and the calcium ionophore A23187, two vasodilators that act by releasing endothelium-derived relaxing factor (EDRF), had no effect on the increased RVR that occurs on reflow. Two inhibitors of EDRF, methylene blue and gossypol, increased RVR in nonischemic kidneys by 45 +/- 6 and 46 +/- 11%, respectively, an increase that was comparable to that found with ischemia alone (55 +/- 7%). The increase in RVR found with the combination of EDRF inhibition and ischemia (59 +/- 5%) was the same as that found with ischemia alone. We conclude that EDRF activity is impaired following ischemia and reperfusion. This abnormality in EDRF may be an important mechanism contributing to postischemic vasoconstriction in the renal vasculature.

Normal aging is accompanied by renal functional and structural deterioration. To examine the hemodynamic and growth-related mechanisms of age-associated nephron loss, as well as the potential beneficial effects of antihypertensive therapy, studies were performed in normal aging Munich-Wistar rats, and in rats receiving long-term antihypertensive therapy with the converting enzyme inhibitor (CEI) enalapril. In protocol 1, rats were treated from the age of 3 mo. Compared with young rats, untreated old rats studied at 2.5 yr of age exhibited normal blood pressure but increased glomerular capillary pressure due to a reduction in afferent arteriolar resistance. Glomerular size increased proportionately to changes in body weight, while kidney weight increased to a lesser degree. Albuminuria rose significantly after 10 mo of age and was accompanied by development of modest, but significant, glomerular sclerosis. CEI therapy from the age of 3 mo lowered systemic and glomerular capillary pressures, did not affect glomerular size, and significantly ameliorated development of albuminuria and structural injury. In protocol 2, untreated rats were compared with a treated group in which enalapril therapy was delayed until the age of 1 yr, when albuminuria was already rising. Subsequent increases in albuminuria and development of sclerosis were significantly attenuated, although not entirely prevented. These findings suggest that hemodynamic maladaptations may contribute to age-related loss of renal function in the rat and that antihypertensive therapy may serve to delay this process.

Fluid (sodium) reabsorption, total glucose efflux, and reabsorption of angiotensin II and insulin from the proximal convoluted tubule were studied in rats by in vivo microperfusion. After 35 min of total renal artery occlusion, function was assessed at two intervals, 0-1 h (early recovery, ER) and 2-4 h (late recovery, LR). Light and electron microscopic evaluation showed 60-75% loss of proximal convoluted tubule brush border membrane in ER and nearly complete restoration of brush border in LR. No other structural abnormalities were evident. Renal blood flow was unchanged from control during both ER and LR. During ER, fluid reabsorption was reduced to 29.8 +/- 5.2%, and total glucose efflux, at normal tubule loads, to 73.9 +/- 5.5% of control. However, angiotensin II and insulin reabsorption were unchanged. In LR, fluid reabsorption remained significantly reduced at 54.3 +/- 8.1% of control. Total glucose efflux from the proximal tubule was normal in LR at glucose loads of up to 400 pmol X min-1, but was significantly reduced at higher loads. Passive glucose efflux, measured in the presence of 10(-4)M phloridzin, was not altered by ischemia. Brief ischemia results in significant alterations in proximal tubular reabsorption of sodium and glucose, which correlate with a substantial loss of brush border during ER. However, despite restoration of cell morphology to normal in LR, transport defects for both sodium and glucose persist.

Micropuncture and morphometric studies related the effects of angiotensin II (ANG II) on glomerular function and structure. Compared with control animals, rats receiving an intrarenal infusion of ANG II at 40 ng.kg-1.min-1 exhibited a marked reduction in the glomerular ultrafiltration coefficient (Kf) (0.84 +/- 0.13 vs. 1.43 +/- 0.05 microliters.s-1.mmHg-1, ANG II vs. control), which caused a decrease in glomerular filtration rate (GFR) (1.04 +/- 0.11 vs. 1.27 +/- 0.11 ml/min) despite an increase in glomerular transcapillary hydraulic pressure difference (46 +/- 1 vs. 40 +/- 1 mmHg). Morphometric studies showed that these hemodynamic changes were not associated with any reduction in glomerular volume (1.27 +/- 0.05 vs. 1.31 +/- 0.07 x 10(6) microns3, ANG II vs. control), glomerular capillary volume (4.25 +/- 0.36 vs. 4.41 +/- 0.33 x 10(5) microns3), or glomerular peripheral capillary surface area (2.24 +/- 0.11 vs. 2.29 +/- 0.30 x 10(5) microns2). Higher-power electron micrographs showed that ANG II also did not alter mean foot process width (478 +/- 14 vs. 491 +/- 18 nm, ANG II vs. control), reduce the total filtration slit length overlying the peripheral capillary wall (7.0 +/- 0.6 vs. 6.6 +/- 0.5 x 10(5) microns), or reduce the average width of individual filtration slits (45 +/- 2 vs. 43 +/- 2 nm). ANG II infusion thus caused a 40% reduction in the value of Kf without causing detectable changes in epithelial cell or filtration slit structure.

No abstract

Myohemoglobinuric acute renal failure (ARF) was induced in dehydrated, salt-deficient, salt-loaded, and untreated rats by intramuscular injection of glycerol, and the renal vasculature was studied after 24 hours. Kidneys were prepared for examination by rapid freezing in vivo to -160 degrees C and freeze substitution in -80 degrees C alcohol, and by perfusion fixation with 1% glutaraldehyde in Ringer's solution at 120 mm Hg. Frozen kidneys were examined by light microscopy after paraffin and epoxy resin embedding. Techniques used in examining the perfusion-fixed kidneys were: (1) vascular injection with silicone rubber and clearing in glycerol, (2) electron microscopy, and (3) morphometric evaluation of lumen to wall area ratios of glomerular arterioles. Kidneys of all rats with ARF showed renal cortical arterial and glomerular arteriolar (afferent and efferent) vasoconstriction. The degree of constriction, estimated by lumen to wall ratios, correlated with the degree of azotemia (r = -0.71; P less than 0.001). Differences between all ARF groups and respective controls were highly significant (P less than 0.001). Vasoconstriction was maximal in the dehydrated group, intermediate in the untreated and Na-deficient rats, and lowest in the salt-loaded animals. Glomerular and peritubular capillaries were patent and free of endothelial swelling or thrombi. Glomerular basement membranes and epithelial foot processes showed no morphological alterations. The observations suggest that marked pre- and postglomerular vasoconstriction occurs in established myohemoglobinuric ARF, that it is related to azotemia, and that mechanical vascular obstruction does not play a major role in this experimental model.