Identification of adrenoceptors and dopamine receptors mediating vascular responses in the superior mesenteric arterial bed of the rat

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Abstract
The nature of the adrenoceptors and dopamine receptors mediating vascular responses in the in-situ blood perfused superior mesenteric arterial bed of the rat have been studied. α1-Adrenoceptor agonists produced vasoconstriction but α2-agonists had no significant effect on vascular resistance. The vasoconstrictor effects of noradrenaline were antagonized by low doses of prazosin (26nmol kg−1 i.v.). Isoprenaline and salbutamol produced vasodilation when the vasculature was preconstricted with arginine vasopressin. The responses to isoprenaline were potently antagonized by propranolol (1.69 μmol kg−1 i.v.) and weakly but significantly reduced by practolol (3.75 μmol kg−1 i.v.) whereas the responses to salbutamol were unaffected by the same dose of practolol. After preconstriction of the vasculature and α-adrenoceptor blockade, dopamine and apomorphine produced dilator responses with both compounds producing the same maximal response and apomorphine being 1.8 times more potent than dopamine. The dopamine responses were present after the animals had been pithed and were resistant to spiperone (506 nmol kg−1 i.v.) but were antagonized by cis-α-flupenthixol (460 nmol kg−1 i.v.). These results suggest that this vascular bed possesses vasoconstrictor α1- but not α2-adrenoceptors, vasodilator β1 and β2-adrenoceptors and vasodilator dopamine receptors which appear similar to the D1-type found centrally.

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