AJP - Heart and Circulatory Physiology, Vol 242, Issue 5 810-H817, Copyright © 1982 by American Physiological Society
Reflex cardiovascular changes with veratridine in the conscious dog
K. W. Barron and V. S. Bishop
The present study was undertaken to examine the reflex responses of
activation of cardiac sensory receptors in the conscious dog. Intracoronary
(left circumflex coronary artery) injection of veratridine (0.10
micrograms/kg) reduced mean arterial pressure (-40 mmHg, P less than 0.05),
heart rate (-34 beats/min, P less than 0.05), and maximum rate of rise of
left ventricular pressure (LV dP/dtmax) (-419 mmHg/s, P less than 0.05).
Bilateral cervical vagal cold block (BVB) eliminated the depressor and
bradycardic responses of veratridine. BVB not only eliminated the negative
inotropic response to veratridine but reversed it to a positive inotropic
response (LV dP/dtmax increased 313 +/- 76 mmHg/s). Ganglionic blockade
abolished all effects of veratridine. The bradycardia and negative
inotropic effects caused by veratridine were attenuated by either atropine
or metoprolol and completely eliminated by the combination of the two
antagonists. Veratridine also produced a decrease in renal artery blood
flow but had no effect on renal vascular resistance. In contrast, iliac
blood flow was increased with veratridine, and this, combined with the
depressor effect, resulted in a decrease in iliac vascular resistance
(-37%), P less than 0.05). BVB abolished the changes in renal and iliac
blood flow or resistance caused by veratridine. The results indicate that
activation of cardiac receptors in the conscious dog elicits inhibitory
reflexes to the heart and peripheral circulation that are mediated by vagal
afferents. After vagotomy, veratridine elicited a reflex positive inotropic
response, which may have resulted from activation of cardiac sympathetic
afferent fibers.
