INTRARENAL BLOOD FLOW DISTRIBUTION AND AUTOREGULATION OF RENAL BLOOD FLOW AND GLOMERULAR FILTRATION RATE

Abstract

Effects of arterial perfusion pressure on renal hemodynamics and correlated changes in distribution of blood flow within the renal cortex were studied in anesthetized dogs. Total renal blood flow to the denervated kidney was measured with an electromagnetic flowmeter and perfusion pressure manipulated by an aortic clamp. Glomerular filtration rate and distribution of cortical blood flow were determined by renal extraction of iothalamate-125I and the radioactive microsphere technique respectively. Autoregulation of renal blood flow was observed till 77mmHg of renal arterial pressure, but glomerular filtration rate declined significantly at pressure levels 102 and 77mmHg, associated with a decrease in the calculated efferent arteriolar resistance. Blood flow rates of four cortical zones of equal thickness differed significantly from each other at normal arterial pressure. Reduction of renal, arterial pressure from 102 to 77mmHg significantly reduced blood flow of the outer cortical zone, but increased that of the inner two cortex zones with concomitant changes of glomerular filtration rate and efferent arteriolar resistance. It was concluded that the characteristic pattern of efferent arteriolar resistance could have been secondary to a redistribution of renal blood flow, i.e., blood perfusing superficial nephrons with relatively high efferent arteriolar resistance was redistributed to inner cortical nephrons characterized by a relatively lower efferent arteriolar resistance. A comparison of the effects of acetylcholine and pressure reduction was made under condition of maximal effectiveness of each intervention. A similarity in response pattern was obtained despite major differences in both interventions. This similarity indicates that flow redistribution seen with pressure reduction is not specific for the autoregulatory process, but is a more general pattern which may depend on intrinsic difference in the responsiveness of the different cortex zones.