AJP - Regulatory, Integrative and Comparative Physiology, Vol 257, Issue 3 635-R640, Copyright © 1989 by American Physiological Society
Subregions of rostral ventral medulla control arterial pressure and regional hemodynamics
B. F. Cox and M. J. Brody
Department of Pharmacology, University of Iowa College of Medicine, Iowa City 52242.
The cardiovascular effects of inactivating rostral ventromedial medulla
(RVMM) under conditions of normal (2.5 ml) and reduced (1.5 ml) tidal
volume were studied in urethan-anesthetized rats. Bilateral microinjection
of lidocaine (200 nl, 4%) reduced mean arterial pressure (MAP), renal,
mesenteric, and particularly hindquarter vascular resistance. These effects
were not significantly altered by reducing tidal volume. Electrical
stimulation of RVMM increased MAP and regional vascular resistances, again
with the hindquarter change most prominent. The integrated cardiovascular
response to stimulating rostral ventrolateral medulla (RVLM) appears to
require integrity of RVMM; however, the converse is not true. Overall,
these studies indicate that 1) the potential for RVMM to maintain
neurogenic control of arterial pressure is as great as RVLM; 2) RVMM is
capable of playing a proportionally greater role in the controlling
hindquarter vascular resistance; 3) the integrity of RVMM appears to be
important for responses elicited from RVLM; and 4) unlike RVLM, neural
control of arterial pressure is sustained by RVMM under conditions of
reduced tidal volume. We conclude that RVLM and RVMM are functionally and
anatomically distinct subregions of rostral ventral medulla with equivalent
capacity to maintain vasomotor tone.
