AJP - Regulatory, Integrative and Comparative Physiology, Vol 267, Issue 2 569-R578, Copyright © 1994 by American Physiological Society
Regulation of central vascular blood flow in the turtle
S. G. Comeau and J. W. Hicks
Division of Physiology, School of Medicine, Creighton University, Omaha, Nebraska 68178.
The purpose of this study was to determine the effects of vagal nerve
stimulation on the pulmonary and systemic circulations in the turtle
Pseudemys scripta. The heart rate (HR), systemic vascular resistance
(Rsys), pulmonary vascular resistance (Rpul), total pulmonary blood flow
(Qpul), and total systemic blood flow (Qsys) were measured during
electrical stimulation of the vagal efferent and the vagal afferent nerves.
Vagal efferent nerve stimulation resulted in a bradycardia, increased Rsys
and Rpul, and a 60% reduction in the Qpul and Qsys. These cardiovascular
changes were eliminated after an intravenous injection of atropine. In
contrast, vagal afferent nerve stimulation resulted in a tachycardia, a
twofold increase in Rsys, a reduction in Rpul, and an 85% increase in Qpul.
These changes were eliminated after pretreating the animals with bretylium
tosylate (10 mg/kg). An intravenous infusion of epinephrine (0.1
micrograms/kg) produced cardiovascular changes similar to vagal afferent
stimulation. The cardiovascular changes resulting from afferent and
efferent nerve stimulation were similar to the cardiovascular adjustments
often associated with intermittent lung ventilation in reptiles. The
results of our study suggest that such cardiovascular changes are under
cholinergic and adrenergic control.
