AJP - Heart and Circulatory Physiology, Vol 257, Issue 5 1498-H1506, Copyright © 1989 by American Physiological Society
Peripheral baroreceptor control of neurohypophysial blood flow during hemorrhage
L. M. Vella, D. F. Hanley, D. A. Wilson and R. J. Traystman
Department of Anesthesiology/Critical Care Medicine, Johns Hopkins Medical Institutions, Baltimore, Maryland 21205.
We measured neurohypophysial blood flow (NHBF) in dogs made hypotensive to
study the time course of neurohypophysial autoregulation. We found that the
neurohypophysis has a unique autoregulatory response in which blood flow
increases transiently before establishing a stable perfusion level. During
the "hyperemic" phase, the time course of the flow transient correlates
with an increased plasma arginine vasopressin (pAVP) neurosecretory
transient. However, unlike pAVP, blood flow does not remain elevated. The
transitory nature of the flow response led us to evaluate the hypothesis
that peripheral baroreceptor activity may be responsible for the hyperemic
phase. Bilateral vagotomy and carotid sinus nerve denervation attenuated
the increase in neural lobe blood flow (NLBF) to a standardized step to 80
mmHg mean arterial pressure. The pAVP response was enhanced both by
vagotomy and carotid sinus denervation. Combined denervation abolished both
the pAVP and the NLBF responses. We conclude that NHBF is autoregulated;
however, control may be exerted at multiple levels, i.e., via nerves as
well as local metabolic mechanisms. The peripheral baroreceptors influence
NHBF primarily during periods of changing blood pressure. When blood
pressure is stable, local mechanisms appear to be dominant.
