Pharmacological characterization of postjunctional α‐adrenoceptors in isolated human omental arteries and veins

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Abstract
The α‐adrenoceptors in human omental arteries and veins were characterized and compared. In the arteries both prazosin (pA29.48) and rauwolscine (pA27.19) displaced the noradrenaline (NA) concentration‐response (cr) curve towards higher concentrations without reduction of maximum. Neither clonidine, nor oxymetazoline had any consistent contractile effects. Phenylephrine had a lower potency than NA, but a similar intrinsic activity. In the veins, both prazosin (pA29.72) and rauwolscine (pA28.11) displaced the NA cr‐curve towards higher concentrations, but also significantly depressed maximum. Clonidine and oxymetazoline contracted veins from 3 out of 7 and 4 out of 6 patients, respectively. Their pD2‐values were similar to that of NA, but their intrinsic activities were significantly lower. NA was more potent than phenylephrine in these vessels, and there was no significant difference in intrinsic activity. The results suggest that in human omental arteries, the postjunctional a‐adrenoceptors are mainly of the α1‐type, even if a small population of α2‐adrenoceptors cannot be excluded. In omental veins, there seems to be a functionally important population of postjunctional α2‐adrenoceptors occurring together with a population of α1‐adrenoceptors.