Functional characteristics of alpha adrenergic and endothelinergic receptors in pressurized rat mesenteric veins

Abstract

Increasing transmural pressure can alter the functional role of post-junctional receptor subtypes. Under conditions of changing transmural pressure, we investigated the relative contributions of alpha adrenergic (α-ARs) and endothelinergic receptors to norepinephrine (NE) and endothelin (ET-1) contractile responses, respectively, in third-order rat mesenteric small veins (MSV) and arteries (MSA). NE, phenylephrine (PE), clonidine, and ET-1 concentration–response curves were constructed in the absence and presence of α-adrenergic and ET-1 receptor antagonists, respectively. MSV were more sensitive to NE, PE, and ET-1 compared with MSA. The sensitivity of MSV to NE was higher than that to PE. Phentolamine (α1-AR/α2-AR antagonist) and prazosin (α1-AR antagonist) completely abolished NE responses. Yohimbine (α2-AR antagonist) reduced NE and clonidine contractile responses in MSV. Clonidine contractile responses were reduced by prazosin in MSA. In MSA and MSV, BQ-610 (ETA receptor antagonist) but not BQ-788 (ETB receptor antagonist) reduced ET-1 contractile responses. Combined application of BQ-610 and BQ-788 caused further reduction in ET-1 concentration–response curves obtained in MSV. These results suggest that in addition to α1-ARs and ETA receptors, α2-ARs and ETB receptors also mediate NE and ET-1 contractile responses in MSV, respectively, with no change in the participation of these receptors as transmural pressure is increased.