Blockade of angiotensin receptors in rat rostral ventrolateral
medulla severely reduces sympathetic vasomotor tone.
Ito, Satoru, and Alan F. Sved.
Department of Neuroscience, University of Pittsburgh, Pittsburgh,
PA
APStracts 3:0111R, 1996.
The rostral ventrolateral medulla (RVLM) plays a primary role in the
tonic and phasic control of arterial blood pressure. Stimulation of
angiotensin receptors in this region appears to contribute to the
tonic excitatory drive of RVLM neurons involved in the control of
blood pressure, but the extent of this contribution has not been
previously evaluated. The present study used bilateral
microinjections of angiotensin receptor antagonists into the RVLM of
chloralose-anesthetized rats to determine the degree to which tonic
blood pressure was dependent upon this angiotensin-mediated input.
Bilateral injection into the RVLM of 1 nmol of Sar1,Thr8-angiotensin
II or Sar1,Ile8-angiotensin II decreased blood pressure approximately
40 mm Hg. The decrease in blood pressure elicited by these
angiotensin antagonists was nearly as great as that elicited by
complete bilateral inhibition of the RVLM produced by local
injections of muscimol or elicited by inhibition of the autonomic
nervous system by intravenous injection of chlorisondamine. The
decrease in blood pressure caused by injection of these angiotensin
antagonists was localized to the RVLM and was dose-related. Responses
elicited by Sar1,Thr8-angiotensin II were eliminated by co-injection
of angiotensin. In addition to markedly decreasing resting blood
pressure, 1 nmol of Sar1,Thr8-angiotensin II injected into the RVLM
also completely antagonized the increase in blood pressure elicited
by blocking the tonic inhibitory influence exerted on the RVLM by
neurons in the caudal ventrolateral medulla. These results
demonstrate that tonic stimulation of angiotensin receptors in the
RVLM accounts for much of the excitatory sympathetic vasomotor drive
emanating from the RVLM.
Received 16 October 1995; accepted in final form 29 December
1995.
APS Manuscript Number R650-5.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 27 March 96