AJP - Regulatory, Integrative and Comparative Physiology, Vol 264, Issue 3 578-R583, Copyright © 1993 by American Physiological Society
Relationship between renal perfusion pressure and blood flow in different regions of the kidney
D. L. Mattson, S. Lu, R. J. Roman and A. W. Cowley Jr
Department of Physiology, Medical College of Wisconsin, Milwaukee 53226.
The present study examined the autoregulation of blood flow in different
regions of the renal cortex and medulla in volume-expanded or hydropenic
anesthetized rats. Blood flow was measured in the whole kidney by
electromagnetic flowmetry, in the superficial cortex with implanted fibers
and external probes for laser-Doppler flowmetry, and in the deep cortex and
inner and outer medulla with implanted fibers for laser-Doppler flowmetry.
At renal perfusion pressure > 100 mmHg, renal blood flow, superficial
cortical blood flow, and deep cortical blood flow were all very well
autoregulated in both volume-expanded and hydropenic rats. Inner and outer
medullary blood flow were also well autoregulated in hydropenia, but blood
flow in these regions was very poorly autoregulated in volume-expanded
animals. As renal perfusion pressure was decreased below 100 mmHg in
volume-expanded and hydropenic animals, renal blood flow, superficial and
deep cortical blood flow, and inner and outer medullary blood flow all
decreased. The results of these experiments demonstrate that blood flow in
both the inner and outer portions of the renal medulla of the kidney is
poorly autoregulated in volume-expanded rats but well autoregulated in
hydropenic animals. In contrast, blood flow in all regions of the renal
cortex is well autoregulated in both volume-expanded and hydropenic
animals. These results suggest that changes in resistance in the
postglomerular circulation of deep nephrons are responsible for the poor
autoregulation of medullary blood flow in volume expansion despite well
autoregulated cortical blood flow.
