Control of rat renal vascular resistance at reduced perfusion pressure

Cellular distribution of exogenous aprotinin in the rat kidney

Aprotinin, an inhibitor of the enzymatic activity of kallikrein in vitro, has been used to study the possible contributions of the kallikrein-kinin systems to physiological and pathological conditions. Pharmacokinetic studies indicate that aprotinin is concentrated in the kidney; however, there is little information with regard to its cellular distribution. The purpose of the present work was to study the cellular distribution of aprotinin, which would be valuable for a better understanding of its intrarenal effects. Sprague-Dawley rats (200-250g, n = 36) received aprotinin (50000 KIU/rat) and were killed at different intervals after its administration. The kidneys were examined histologically and the cellular distribution of aprotinin was studied by immunohistochemistry. Aprotinin was localized at 30 min concentrated within vesicles in the apical border of the proximal tubule cells. Later (2 h) it was observed distributed over the cytoplasm, where it remained for the 24 h studied. Aprotinin was also detected in connecting tubule cells colocalized with kallikrein, and in the basal portion of collecting tubule cells. No evidence of endogenous aprotinin was observed. The binding of aprotinin to the connecting tubule cells and collecting ducts offers a partial explanation of its renal effects.

Studies of renal autoregulation in pancreatectomized and streptozotocin diabetic rats

We studied renal autoregulation in pancreatectomized Munich-Wistar diabetic rats and in their sham-operated controls. In a second experiment we studied renal autoregulation in untreated and insulin treated streptozotocin diabetic Munich-Wistar rats and their nondiabetic controls. In the first experiment the diabetic rats had higher baseline renal blood flows (RBF). There was a fall in renal vascular resistance (RVR) and sustained RBF in both diabetic and control rats as renal perfusion pressures (RPP) was reduced from 130 and 110 mm Hg. As RPP was reduced from 110 and 80 mm Hg, there was no significant Change in RVR in control rats and RBF began to fall. Below RPP of 80 mm Hg RVR rose and RBF fell sharply in these rats. In contrast, there was a progressive fall in RVR as RPP was lowered to 60 mm Hg in the diabetic rats and, thus, RBF was much better sustained in these animals. In the second experiment the plasma glucose level was 502 +/- 52 mg/dl (X +/- SD) in the untreated diabetic rats and only modestly reduced to 411 +/- 49 mg/dl in the insulin treated animals. Untreated streptozotocin diabetic rats had moderately reduced and insulin-treated diabetic rats had mildly reduced baseline RVR and RBF. However, in these animals as in the pancreatectomized rats the increases in RVR noted in control rats at subautoregulatory RPPs were not seen. Thus, regardless of whether baseline RBFs were increased or decreased, diabetic rats sustained RBF at markedly reduced RPPs far more efficiently than did nondiabetic rats. The pathogenesis of these abnormalities in diabetic rats was not learned in these studies.(ABSTRACT TRUNCATED AT 250 WORDS)

Urinary and proximal tubule acidification during reduction of renal blood flow in the rat

1. The effects of reduction in renal blood flow (RBF) on urinary acidification and proximal tubule H+ ion secretion were studied after partial aortic clamping in rats. 2. Acute reduction of the renal perfusion pressure (from 109 +/- 3.88 to 77.4 +/- 1.05 mmHg) decreased both inulin and PAH (p-aminohippurate) clearances to about one-third of their control values. Absolute levels of urinary sodium excretion also decreased markedly, but fractional sodium excretion did not change significantly. 3. Urine pH and bicarbonate levels were not affected, but titratable acidity increased significantly from 0.12 +/- 0.011 to 0.25 +/- 0.042 muequiv min-1 ml-1 glomerular filtration rate (GFR). During aortic clamping, cortical PCO2 as determined by means of Severinghaus microelectrodes was reduced by a mean value of 7.0 +/- 1.5 mmHg. 4. Proximal tubule acidification kinetics were studied by stationary microperfusion techniques in which the time course of pH changes was monitored by pH microelectrodes. Steady-state pH fell from a mean control value of 6.77 +/- 0.03 to 6.65 +/- 0.02, and stationary bicarbonate concentrations from 4.70 +/- 0.27 to 2.84 +/- 0.18 mM. Acidification half-time decreased from 5.07 +/- 0.30 to 4.39 +/- 0.19 s, and net bicarbonate reabsorption increased from 1.63 +/- 0.14 to 1.99 +/- 0.12 nmol cm-2 s-1, these changes being statistically significant. 5. The experiments demonstrate that both overall acid excretion and proximal acid secretion are not compromised by a large decrease of RBF to about one-third of the control value; titratable acid excretion and proximal net bicarbonate reabsorption were even moderately increased under these conditions.

Effect of the protease inhibitor aprotinin on renal hemodynamics in the pig

Aprotinin, the serine protease inhibitor that also inhibits glandular (urinary) kallikrein, or vehicle was infused into the aorta above the renal arteries of anesthetized pigs. Renal hemodynamic and functional parameters were followed over time and during hemorrhagic hypotension. Both renal cortical blood flow and glomerular filtration rate were maintained in vehicle-treated animals at mean arterial pressures as low as 70 mm Hg. As long as renal cortical blood flow and glomerular filtration rate were maintained during the progressive hypotension, urinary excretion rate of kallikrein (as defined by kinin-generating activity) was increased. In contrast, all aprotinin-treated animals had a decreased excretion rate, and the renal cortical blood flow declined with the mean arterial pressure during hemorrhage. The pattern of glomerular filtration rate and plasma renin activity was comparable in both aprotinin-treated and vehicle-treated hemorrhaged animals. Our findings suggest that the endogenous renal kallikrein-kinin system is required for functional renal vasodilatation to maintain renal cortical blood flow during hemorrhage and is therefore directly or indirectly responsible for adjustment of preglomerular resistance.

The effect of pressor doses of Angiotensin II on autoregulation and intrarenal distribution of glomerular filtration rate in the rat

This study was designed to investigate the effect of pressor doses of exogenous Angiotensin II (AII) on autoregulation and intrarenal distribution of single nephron glomerular filtration rate (SNGFR) in anesthetized, normotensive rats. SNGFR at all cortical levels of the left kidney was measured with a modified Hanssen technique at three renal arterial pressures (RAP): Spontaneous, 100 +/- 1 mmHg and 70 +/- 1 mmHg. In control rats, both outer cortical (OC) and inner cortical (IC) nephrons showed complete autoregulation of SNGFR when RAP was reduced to 100 +/- 1 mmHg. Further reduction to 70 +/- 1 mmHg resulted in different responses among the cortical layers, accompanying a decrease in SNGFR. The SNGFRIC/SNGFROC ratio increased from 1.36 +/- 0.053 to 1.52 +/- 0.047 and a fractional redistribution of glomerular filtration rate towards IC nephrons was seen. When the kidney was submitted to a RAP of 70 +/- 1 mmHg, there was a concomitant increase in central arterial pressure (CAP) from 120 +/- 4.3 to 134 +/- 3.2 mmHg. A continuous i.v. infusion of AII (0.5 microgram . min-1 . kg-1 BW) increased mean arterial pressure from 123 +/- 1.4 to 142 +/- 3.8 mmHg, an effect corresponding to that on peripheral vascular resistance during reduction of RAP to 70 +/- 1 mmHg in control rats. This dose reduced SNGFR at all cortical levels, but did not per se lead to redistribution of SNGFR. A reduction in RAP to 100 +/- 1 mmHg during AII administration resulted in impaired autoregulation of SNGFR in both OC and IC nephrons.(ABSTRACT TRUNCATED AT 250 WORDS)