Regional vasodilation to endothelin-1 is mediated by a non-ETA receptor subtype in the anaesthetized rat: effect of BQ-123 on systemic haemodynamic responses.

The sustained infusion of 75 nmol/kg per min BQ-123 selectively attenuates the systemic pressor responses to i.v. bolus endothelin-1 in the anaesthetized rat; the initial systemic vasodepression is only attenuated when a 10-fold higher dose of this ETA-selective antagonist is infused. These doses of BQ-123 do not antagonize the haemodynamic actions of angiotensin II or calcitonin gene-related peptide nor do they alter basal systemic haemodynamics. The secondary increase in carotid vascular resistance associated with the systemic pressor actions of endothelin-1 is selectively attenuated by the bolus i.v. administration of BQ-123 (1.6 mumol/kg); the maximum degree of the vasorelaxation that precedes this more sustained constriction is unaltered. Thus, the initial carotid vasodilation observed to endothelin-1, and the associated systemic vasodepression, is mediated by a non-ETA receptor subtype. Furthermore, subtle differences might exist between the receptors mediating mesenteric and carotid vasoconstriction since only the latter is sensitive to BQ-123.