Vagal and sympathetic components of the heart rate reflex in
chronic portal vein stenosis.
Battarbee, Harold D., James H. Zavecz, and Kenneth W. Betzing.
Departments of Physiology and Pharmacology, Louisiana State
University Medical Center, Shreveport, LA 71130
APStracts 2:0163G, 1995.
Portal Hypertension and portosystemic shunting's effects on autonomic
components of the heart rate (HR) baroreflex and on skeletal muscle
blood flow changes were investigated using the chronic portal vein
-stenosed rat. Phenylephrine- and Na nitroprusside-induced changes in
mean arterial pressure (MAP), HR, and skeletal muscle conductance
(SMC) were assessed before and after muscarinic or [beta]
-adrenoceptor blockade. Stenosed rats' MAP were less than sham
-operated rats' (90 +/- 3 mmHg vs 81 +/- 2 mmHg, P<0.05), and
their portal pressures were increased (7.4 +/- 0.5 mmHg vs 13.9 +/-
1.0 mmHg, P<0.005). Stenosed animals' phenylephrine pressor
responses were reduced, their associated bradycardic responses were
enhanced (-1.912 +/- 0.109 BPM/mmHg vs -1.427 +/- 0.148 BPM/mmHg, P
<0.01), and their SMC responses were diminished. Methylatropine
abolished bradycardic responses and enhanced pressor responses,
without affecting SMC. Following propranolol, stenosed rats' reflex
bradycardic responses were less than in shams (-0.492 +/- 0.085
BPM/mmHg vs -0.738 +/- 0.058 BPM/mmHg, P<0.01), and their
pressor and SMC responses became indistinguishable from shams. In
contrast, tachycardic responses to nitroprusside-induced hypotension
before propranolol were impaired in stenosed rats (-1.492 +/- 0.114
BPM/mmHg vs -2.225 +/- 0.347 BPM/mmHg, P<0.05), and their SMC
responses were reduced. Muscarinic blockade did not affect HR or SMC
responses to hypotension in either stenosed or sham rats. [beta]
-Adrenoceptor blockade, however, prevented hypotension-induced
tachycardia, enhanced nitroprusside's depressor responses, and
eliminated the between-group differences in SMC responses. These
studies indicate that increased gain of the parasympathetic limb of
the cardiac baroreflex was responsible for attenuated pressor
responses to phenylephrine in portal vein-stenosed animals and that
[beta]-adrenoceptors contributed to their skeletal muscle vascular
hyporesponsiveness to phenylephrine. Altered [beta]-adrenoceptor
function also appears to contribute to impaired chronotropic and
skeletal muscle conductance responses to hypotension.
Received 22 February 1994; accepted in final form 16 June 1995.
APS Manuscript Number G73-4.
Article publication pending Am. J. Physiol. (Gastrointest. Liver
Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 14 August 1995.