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

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Abstract
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 was studied. SNGFR at all cortical levels of the left kidney was measured with a modified Hanssen technique at 3 renal arterial pressures (RAP): spontaneous, 100 .+-. 1 mm Hg and 70 .+-. 1 mm Hg. In control rats, both outer cortical (OC) and inner cortical (IC) nephrons showed complete autoregulation of SNGFR when RAP was reduced to 100 .+-. mm Hg. Further reduction to 70 .+-. 1 mm Hg had 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 mm Hg, there was a concomitant increase in central arterial pressure (CAP) from 120 .+-. 4.3 to 134 .+-. 3.2 mm Hg. A continuous i.v. infusion of AII (0.5 .mu.g .cntdot. min-1 .cntdot. kg-1 BW) increased mean arterial pressure from 123 .+-. 1.4 to 142 .+-. 3.8 mm Hg, an effect corresponding to that on peripheral vascular resistance during reduction of RAP to 70 .+-. 1 mm Hg in control rats. This dose reduced SNGFR at all cortical levels, but did not per se lead to redistribution of SNGFR. A reduction of RAP to 100 .+-. mm Hg during AII administration resulted in impaired autoregulation of SNGFR in both OC and IC nephrons. Exogenous AII apparently impairs autoregulation and cannot per se have an effect mimicking the fractional redistribution seen in control rats with a reduction of RAP below the limit for autoregulation. However, in this situation intrarenally formed AII may still be of importance for autoregulation and distribution of glomerular filtration rate.