AJP - Regulatory, Integrative and Comparative Physiology, Vol 251, Issue 1 23-R31, Copyright © 1986 by American Physiological Society
Increased left ventricular pressure attenuates the baroreflex in unanesthetized dogs
M. J. Holmberg and I. H. Zucker
To determine whether stimulation of left ventricular mechanoreceptors
alters the baroreflex control of heart rate (HR), dogs were instrumented
with a vascular occluder around the ascending aorta and appropriate
instrumentation for the recording of left ventricular pressure (LVP),
aortic pressure, left atrial pressure, HR, and left ventricular dP/dt.
Baroreflex sensitivity (pulse interval or HR vs. aortic systolic pressure
linear-regression slopes to infusions of phenylephrine or nitroprusside)
was determined in the conscious state a minimum of 7 days postoperatively.
After control responses were determined with both phenylephrine and
nitroprusside, the experiment was repeated during inflation of the
ascending aortic occluder so as to significantly raise left ventricle
systolic pressure from 127.9 +/- 8.4 to 178.5 +/- 11.3 mmHg (P less than
0.01) and left ventricle end-diastolic pressure from 3.5 +/- 0.7 to 8.9 +/-
1.0 mmHg (P less than 0.01). There were no changes in mean arterial blood
pressure, pulse pressure, or HR during elevation of LVP. The baroreflex
sensitivity was reduced only during the infusion of nitroprusside from a
control of 11.03 +/- 1.9 to 4.80 +/- 1.2 ms/mmHg (P less than 0.01) for the
pulse interval relationship and from -2.51 +/- 0.53 to -1.14 +/- 0.32 beats
. min-1 . mmHg-1 (P less than 0.05) for the HR relationship. Cholinergic
blockade with atropine abolished the depression in the baroreflex
sensitivity during nitroprusside infusion when LVP was increased. beta
1-Adrenergic blockade with metoprolol did not significantly reduce the
baroreflex sensitivity during increased LVP.(ABSTRACT TRUNCATED AT 250
WORDS)
