| Angiotensin II (AII) and 1-norepinephrine (NE) caused immediate, dose-dependent increases in aortic blood pressure (BP) when injected intravenously into anaesthetized ducks. NE and epinephrine (E) concentrations in arterial plasma were found to be elevated 1 min after injection of AII, when BP was peaking, while plasma levels of free dopamine (DA) did not undergo any consistent change. Depletion of NE and E stores, following treatment with reserpine, diminished pressor responses to AII but did not affect responses to NE. Adrenalectomy lowered plasma levels of NE and E. Adrenalectomy also decreased noradrenergic, adrenergic and pressor responses to AII, but did not diminish pressor responses to NE injections. The pressor action of AII was inhibited in both sham-operated and adrenalectomized ducks by the alpha-adrenergic blocking drug phenoxybenzamine; the blockade of alpha-adrenergic receptors by phenoxybenzamine was incomplete since pressor responses to NE were lessened but not abolished. Acute, chemical sympathectomy with 6-hydroxydopamine (6-OHDA) diminished the noradrenergic and pressor effects of AII in adrenalectomized ducks, and in some cases a drop in BP preceded the pressor phase of the response to AII. Administration of a converting enzyme inhibitor, SQ20881, reduced pressor responses to angiotensin I (AI), but did not affect responses to AII, in 6-OHDA treated adrenalectomized ducks.;The diminished pressor responses to AII in adrenalectomized ducks during alpha-adrenergic blockade or chemical sympathectomy indicated that AII affects extra-adrenal, as well as adrenal sources of catecholamines. Ganglionic blockade by mecamylamine enhanced pressor responses to AII in intact ducks, suggesting that AII acts directly on adrenal chromaffin cells and peripheral nerves.;It was concluded from these experiments that the pressor response to AII in the Pekin duck is mediated by increased levels of NE and E, derived from both adrenal and extra-adrenal stores, and acting on alpha-adrenergic receptors. A survey of the literature indicated that activation of the sympathetic nervous system by AII may mediate cardiovascular responses to AII, to a greater or lesser extent, in species belonging to the classes Chondrichthyes, Osteichthyes, Reptilia, Aves and Mammalia. |
