ROLE OF DORSAL VAGAL MOTOR NUCLEUS IN ANGIOTENSIN II-MEDIATED TACHYCARDIA IN THE CONSCIOUS TROUT ONCORHYNCHUS-MYKISS

Responses of heart rate (HR) and mean arterial blood pressure (MABP) w ere examined following microinjection of angiotensin II ([Asn(1),Val(5 )]AII) within the dorsal vagal motor nucleus (DVN) of the conscious tr out's brainstem. AII (15-125 fmol) preferentially and significantly in creased HR in a dose-dependent manner, but tile rise in MABP was not d ose-dependent and was only significant (P < 0.05) after injection of A II at a dose of 62.5 fmol. The cardiovascular action of AII was site-s pecific, since administrations of the peptide at a dose of 62.5 fmol, but outside the boundaries of the DVN, were devoid of any effect on HR or MABP. All the responses to DVN injections of AII were totally prev ented by DVN injection of 1 nmol of losartan, a mammalian non-peptide AII subtype 1 (AT,) receptor antagonist. The ability of DVN injection of ALI to induce a tachycardic response was negatively correlated to H R basal values. In conclusion, these results indicate that, at femtomo lar doses, AII exerts a central neurocardioregulatory role, involving a localized receptor closely related to the mammalian AT(1) receptor s ubtype within the DVN of the trout. (C) 1997 Elsevier Science B.V.