Total peripheral conductance mediates antihypertensive effect of nonpeptide mixed endothelin receptor antagonist in deoxycorticosterone acetate-salt hypertensive rats

The relative contribution of cardiac output (CO) and total peripheral conductance (TPC) to the changes in blood pressure (BP) evoked by an intravenous injection of bosentan, a nonpeptide mixed endothelin (ET) antagonist, were investigated in conscious unrestrained deoxycorticosterone acetate (DOCA)-salt hypertensive rats and sham-control rats. Blood pressure was recorded by radiotelemetry devices and CO by ultrasonic transit-time now probes. Bosentan significantly reduced BP (from 141 +/- 3 to 111 +/- 3 mm Hg) and increased TPC (from 1.19 +/- 0.1 to 1.72 +/- 0.2 mL/min/kg/mm Hg) in DOCA-salt hypertensive rats, but not in sham rats. An increase in CO opposed the BP-lowering effect of the antagonist. The results demonstrate that the role of ET receptors in the maintenance of the hypertensive state in the DOCA-salt model of hypertension is exerted at the level of the resistance vessels and not on factors that regulate cardiac output. (C) 1999 American Journal of Hypertension, Ltd.