Hypertension induced by blockade of ETB receptors in conscious nonhuman primates: role of ETAreceptors

Abstract

The role of endothelin-B (ETB) receptors in circulatory homeostasis is ambiguous, reflecting vasodilator and constrictor effects ascribed to the receptor and diuretic and natriuretic responses that could oppose the hypertensive effects of ET excess. With the use of conscious, telemetry-instrumented cynomolgus monkeys, we characterized the hypertension produced by ETB blockade and the role of ETA receptors in mediating this response. Mean arterial pressure (MAP) and heart rate (HR) were measured 24 h/day for 24 days under control conditions and during administration of the ETB-selective antagonist A-192621 (0.1, 1.0, and 10 mg/kg bid, 4 days/dose) followed by coadministration of the ETAantagonist atrasentan (5 mg/kg bid) + A-192621 (10 mg/kg bid) for another 4 days. High-dose ETB blockade increased MAP from 79 ± 3 (control) to 87 ± 3 and 89 ± 3 mmHg on the first and fourth day, respectively; HR was unchanged, and plasma ET-1 concentration increased from 2.1 ± 0.3 pg/ml (control) to 7.24 ± 0.99 and 11.03 ± 2.37 pg/ml. Atrasentan + A-192621 (10 mg/kg) decreased MAP from hypertensive levels (89 ± 3) to 75 ± 2 and 71 ± 4 mmHg on the first and fourth day, respectively; plasma ET-1 and HR increased to 26.64 ± 3.72 and 28.65 ± 2.89 pg/ml and 113 ± 5 (control) to 132 ± 5 and 133 ± 7 beats/min. Thus systemic ETB blockade produces a sustained hypertension in conscious nonhuman primates, which is mediated by ETA receptors. These data suggest an importance clearance function for ETB receptors, one that influences arterial pressure homeostasis indirectly by reducing plasma ET-1 levels and minimizing ETA activation.