Abstract
Blockade of angiotensin II (Ang II) function during 8 days of oral therapy with lisinopril (20 mg/kg) and losartan (10 mg/kg) normalized the arterial pressure (112+/-3/70+/-3 mm Hg) and raised the plasma concentrations of the vasodilator peptide angiotensin-(1-7) [Ang-(1-7)] of 21 male spontaneously hypertensive rats (SHR). Treated animals were then given a 15-minute infusion of either mouse immunoglobulin G1 or a specific monoclonal Ang-(1-7) antibody while their blood pressure and heart rate were recorded continuously in the awake state. The concentrations of Ang II and Ang-(1-7) in arterial blood were determined by radioimmunoassay. Infusion of the Ang-(1-7) antibody caused significant elevations in mean arterial pressure that were sustained for the duration of the infusion and were accompanied by transient bradycardia. Although the hemodynamic effects produced by infusion of the Ang-(1-7) antibody had no effect on plasma levels of Ang II, they caused a twofold rise in the plasma concentrations of Ang-(1-7). A pressor response of similar magnitude and characteristics was obtained in a separate group of SHR treated with the combination of lisinopril and losartan for 8 days during an infusion of [Sar1-Thr8]Ang II. The pressor response induced by the administration of this competitive, non-subtype-selective Ang II receptor blocker was not modified by pretreatment of the rats with an angiotensin type-2 (AT2) receptor blocker (PD123319). Plasma concentrations of Ang II and Ang-(1-7) were not changed by the administration of [Sar1-Thr8]Ang II either in the absence or in the presence of PD123319 pretreatment. These results are the first to indicate an important contribution of Ang-(1-7) in mediating the vasodilator effects caused by combined inhibition of angiotensin-converting enzyme and AT1 receptors. The comparable results obtained by administration of [Sar1-Thr8]Ang II suggest that the vasodepressor effects of Ang-(1-7) during the combined treatment is modulated by a non-AT1/AT2 angiotensin subtype receptor.
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