AJP - Regulatory, Integrative and Comparative Physiology, Vol 244, Issue 4 544-R552, Copyright © 1983 by American Physiological Society
Arterial baroreceptor reflex control of heart rate in two species of turtle
G. A. Stephens, H. W. Shirer, J. W. Trank and K. L. Goetz
Attempts were made to stimulate an arterial baroreceptor reflex in
anesthetized and conscious pond turtles. In turtles anesthetized with
either alpha-chloralose or pentobarbital, occlusion of the ascending or
descending aortas produced no reflex heart rate (HR) changes. In
pentobarbital-anesthetized turtles, direct electrical or mechanical
stimulation of potential baroreceptor sites along the central aortic arches
and carotid arteries produced no significant changes in either HR or blood
pressure (BP). Occlusion of the common carotid arteries also produced no HR
or BP changes. Intravenously administered nitroglycerin lowered BP but
caused no reflex tachycardia in anesthetized turtles. Phenylephrine and
angiotensin elevated BP in the anesthetized turtle but caused no reflex
bradycardia. In conscious turtles phenylephrine increased BP and
nitroglycerin decreased BP. Neither response produced a statistically
significant HR change, although HR tended to decrease transiently with
phenylephrine and increase with nitroglycerin. These HR changes were
abolished by atropine. Rapid intra-arterial infusion of 6% dextran
transiently raised BP but caused no reflex bradycardia. These experiments
suggest that cardiovascular regulation in the turtle is accomplished
without a major contribution from arterial baroreceptor reflexes.
