AJP - Renal Physiology, Vol 259, Issue 4 573-F579, Copyright © 1990 by American Physiological Society
Renal responses to lower body negative pressure in humans
B. Tidgren, P. Hjemdahl, E. Theodorsson and J. Nussberger
Department of Clinical Physiology, Karolinska Hospital, Stockholm, Sweden.
Renal blood flow, renal sympathetic nerve activity, assessed by the renal
overflows of norepinephrine (NE), dopamine (DA), and neuropeptide Y-like
immunoreactivity (NPY-LI), as well as plasma renin activity and angiotensin
II (ANG II) were evaluated during stepwise increases in lower body negative
pressure (LBNP) in 10 healthy volunteers. The fractional extraction of
epinephrine (Epi) was used to assess renal catecholamine removal
(approximately 50%) from arterial plasma. Renal NE, DA, and NPY-LI
overflows at rest were 235 +/- 31, 30 +/- 5, and 0.6 +/- 0.2 pmol/min,
respectively. LBNP increased renal vascular resistance (RVR) by 52% and
renal NE overflow by 31%. Renin release increased by 330% (from 64 +/- 12
units/min) and arterial ANG II levels by 119%, without altering the renal
ANG II extraction (which was approximately 50%). Renal DA and NPY-LI
overflows were unaffected. A "vaso-vagal" reaction in one subject was
associated with cessation of renal NE overflow and marked elevations of
arterial Epi, renal renin release, and arterial ANG II. Selective unloading
of cardiopulmonary baroreceptors by low-level LBNP did not affect RVR,
whereas higher levels of LBNP caused renal vasoconstriction probably
mediated in part by increased renal sympathetic nerve activity and in part
by ANG II.
