Role of the renin-angiotensin system in mediating the effects of
posture on renal function.
Reinhart, Glenn A., and Thomas E. Lohmeier.
University of Mississippi Medical Center, Department of Physiology
and Biophysics, 2500 North State Street, Jackson, MS 39216-4505
APStracts 3:0074R, 1996.
This study was designed to quantitate the influence of the
neurohumoral activation associated with orthostatic stress on renal
hemodynamics and sodium excretion, and further, to determine the
importance of the renin-angiotensin system in mediating these changes
in renal function. 7 conscious dogs were studied while lying in the
recumbent position and, subsequently, after standing in a supporting
sling. Experiments were conducted under control conditions and after
plasma angiotensin II (ANG II) concentration was fixed at control
levels by chronic infusion of captopril (14 [mu]g/kg/min) and ANG II
(0.5+/-0.02 ng/kg/min). During control experiments, 45 minutes of
standing increased plasma renin activity two-fold, while mean
arterial pressure, heart rate, and plasma norepinephrine
concentration remained unchanged. During standing, GFR and renal
plasma flow (RPF) fell to 88+/-2 and 77+/-3% of recumbent values,
respectively, while filtration fraction (FF) increased 16+/-1%.
Additionally, urinary (UNaV) and fractional sodium excretion (FENa )
decreased to 27+/-6% and 30+/-7% of recumbent values, respectively.
When plasma ANG II concentration was fixed at control levels during
standing there were no significant changes in GFR, while increments
in FF and reductions in RPF, UNaV, and FENa, were attenuated by 63,
40, 30, and 33%, respectively. These data suggest that in conscious
dogs, standing in a supporting sling causes reflex activation of the
sympathetic nervous and renin-angiotensin systems, eliciting
reductions in GFR, RPF, and urinary sodium excretion. Furthermore,
ANG II contributes significantly to the effects of passive standing
on renal hemodynamics and urinary sodium excretion.
Received 10 September 1995; accepted in final form 23 February
1996.
APS Manuscript Number R561-5.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 13 March 96