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) were examined following microinjection of angiotensin II ([Asn1,Val5]AI) within the dorsal vagal motor nucleus (DVN) of the conscious trout's brainstem. AII (15-125 fmol) preferentially and significantly increased HR in a dose-dependent manner, but the rise in MABP was not dose-dependent and was only significant (P0.05) after injection of AII at a dose of 62.5 fmol. The cardiovascular action of AII was site-specific, 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 prevented by DVN injection of 1 nmol of losartan, a mammalian non-peptide AII subtype 1 (AT1) receptor antagonist. The ability of DVN injection of AII to induce a tachycardic response was negatively correlated to HR basal values. In conclusion, these results indicate that, at femtomolar doses, AII exerts a central neurocardioregulatory role, involving a localized receptor closely related to the mammalian AT1 receptor subtype within the DVN of the trout.