CONTRACTION-MEDIATING α-ADRENORECEPTORS IN ISOLATED HUMAN OMENTAL, TEMPORAL AND PIAL ARTERIES

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Abstract
The .alpha.-adrenoreceptors mediating contraction in human omental (OA). temporal (TA) and pial (PA) arteries obtained during surgery were characterized by means of subtype selective agonists and antagonists. In the OA and TA, prazosin concentration-dependently shifted the noradrenaline [norepinephrine] (NA) concentration-response (cr) curve towards higher concentrations, without depression of maximum. The corresponding Schild plots had slopes close to unity. Also rauwolscine caused a rightward displacement of the NA cr-curve in both OA and TA, without affecting the maximum response. In the TA, rauwolscine in concentrations below 3 .times. 10-6 M appeared to be unable to shift the NA cr-curve. In the OA, rauwolscine 3 .times. 10-8 M shifted the curve and the Schild plot seemed to be biphasic. Oxymetazoline, but not clonidine, produced contractile responses in the TA and OA and phenylephrine was a full agonist in both types of vessel. The PA showed a pronounced inter- and intra-individual variation in the response to NA, and often exhibited spontaneous activity. Prazosin was considerably more effective than rauwolscine and yohimbine to inhibit NA-induced responses. Clonidine had no contractant effect, whereas oxymetazoline was more and phenylephrine less potent than NA. In human OA and TA and PA, the .alpha.-adrenoreceptor mediating contraction is apparently mainly of the .alpha.1-type.