Effect of Ganglionic Blockade on Pressor Responses to Angiotensin II during Converting Enzyme Inhibition

Dose-response curves to angiotensin II were consecutively performed in rats after anesthesia (pentobarbital 60 mg/kg ip), converting enzyme inhibition (SQ14225 1 mg/kg iv), and ganglionic blockade (pentolinium 10 mg/kg sc) to explore the participation of the sympathetic nervous system in the immediate pressor action of the peptide. Experiments were conducted after the animals were maintained on a sodium-deficient diet for 2 weeks. Converting enzyme inhibition was maintained during ganglionic blockade to avoid changes in the circulating level of endogenous angiotensin II which might be caused by the latter maneuver. SQ14225 caused a 35 ± 4 mm Hg (P < 0.001) fall in systolic pressure and a significant shift to the left of the dose-response curve to angiotensin II compared to that obtained after anesthesia alone. In contrast, pentolinium did not further modify responses to angiotensin II despite significantly lowering systolic blood pressure 49 ± 5 mm Hg (P < 0.001). Our data confirm that a major determinant for the response to injected angiotensin II is the prevailing circulating level of the peptide and suggest that a direct effect of angiotensin II on the vascular bed is the most likely mechanism of action in the whole animal, since an intact sympathetic tone is not required for the peptide to evoke its full pressor response.