AJP - Regulatory, Integrative and Comparative Physiology, Vol 269, Issue 3 726-R735, Copyright © 1995 by American Physiological Society
Angiotensin II and cardiovascular regulation in a freshwater teleost, Anguilla rostrata LeSueur
G. Y. Oudit and D. G. Butler
Department of Zoology, University of Toronto, Ontario, Canada.
Cardiac output (CO), dorsal aortic blood flow (BFDA) and blood pressure
(PDA), and heart rate (HR) were recorded simultaneously in conscious
freshwater eels. Physiological doses of [Asn1,Val5]angiotensin II (ANG II;
25-150 ng/kg iv) were used to investigate its effects on the blood flow
[CO, BFDA, and estimated branchial shunting (BS)] and systemic vascular
resistance (RSys) components of the pressor response and possible
mechanism(s) of action. CO was increased mainly by an elevated stroke
volume (SV) due to positive inotropy and/or Frank-Starling principle in a
dose-related manner. An intact baroreceptor reflex attenuated the blood
flow increase by 25% via the inhibitory cardiac vagal innervation. The
elevation in estimated BS was a passive response to the increased CO, since
the proportion of CO perfusing the pathway remained constant. PDA showed a
similar dose-dependent increase in response to ANG II but the peak PDA
preceded the peak CO responses at all doses; RSys was only transiently
elevated at peak PDA. The increase in blood flow was an important
contributor to the vasopressor responses. Alpha-Adrenergic blockade
partially inhibited the pressor effect of ANG II (100 ng/kg) primarily by
attenuating the increase in blood flow (50-70%). The data provide evidence
for an ANG II-mediated cardiovascular control in teleosts directly and
indirectly via catecholamine release.
