AJP - Heart and Circulatory Physiology, Vol 248, Issue 6 835-H842, Copyright © 1985 by American Physiological Society
Autoregulation of capillary pressure and filtration rate in isolated rat hindquarters
R. J. Korthuis, D. N. Granger, M. I. Townsley and A. E. Taylor
The hypothesis that skeletal muscle capillary pressure and/or capillary
filtration rate are autoregulated was tested in 10 isolated rat
hindquarters. Capillary pressure was directly assessed with the venous
occlusion technique as abdominal aortic pressure was reduced in 25-mmHg
decrements from 125 to 25 mmHg. Capillary pressure was not altered by
reduction of arterial pressure from 125 to 100 mmHg, but it decreased
progressively when arterial pressure was reduced from 100 to 25 mmHg. As
perfusion pressure was reduced, capillary filtration rate decreased
progressively, while the capillary filtration coefficient increased. The
progressive decrease in capillary pressures was less than that predicted
for a totally passive system, implying that capillary pressure was
autoregulated to some degree. However, analysis of pre- to postcapillary
resistance ratios suggested that the degree of capillary pressure
autoregulation was minimal when perfusion pressures varied over a range of
100-25 mmHg. Capillary filtration rate was maintained better than would be
predicted from the measured fall in capillary pressure by readjustments of
interstitial Starling forces. These results indicate that capillary
pressure is poorly autoregulated in rat skeletal muscle but that
compensatory readjustments in interstitial Starling forces help maintain
fluid balance and prevent excess dehydration of the interstitium of
skeletal muscle as arterial pressure is reduced.
