Contraction-mediating alpha-adrenoreceptors in isolated human omental, temporal and pial arteries.

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 OAs and TAs, prazosin concentration-dependently shifted the noradrenaline (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 OAs and TAs, without affecting the maximum response. In the TAs, OAs, rauwolscine 3 x 10(-8) M shifted the curve and the Schild plot seemed to be biphasic. Oxymetazoline, but not clonidine, produced contractile responses in the TAs and OAs, and phenylephrine was a full agonist in both types of vessel. The PAs 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. It is concluded that in human OAs, TAs and PAs, the alpha-adrenoreceptor mediating contraction is mainly of the alpha 1-type.