Angiotensin II and cardiovascular regulation in a freshwater teleost, Anguilla rostrata LeSueur.

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.