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Effect of diltiazem upon contractile responses to phenylephrine, cirazoline, Sgd 101/75, St 587 and B-HT 920 in rabbit aorta and dog saphenous vein preparations

1986; Elsevier BV; Volume: 121; Issue: 3 Linguagem: Inglês

10.1016/0014-2999(86)90252-9

1879-0712

Josep Bou, R. Massingham,

Pharmacological Effects and Assays

Diltiazem (10 μM) did not significantly affect concentration-response curves to the full, relatively selective α1-adrenoceptor agonists phenylephirne and cirazoline in rabbit aorta and dog saphenous vein preparations. The effects of these 2 agonists remained resistant to diltiazem even in tissues pretreated with phenoxybenzamine (0.03 or 0.1 μM, 20 min) to reduce the α-adrenoceptor reserve. Sgd 101/75 and St 587 were partial agonists in both vascular preparations. The concentration-response curves to these relatively selective α1-adrenoceptor agonists were also unaffected, or only slightly attenuated, by diltiazem. B-HT 920 at low concentrations preferentially stimulated the dog saphenous vein preparation and only at high concentrations elicited small contractions of the rabbit aorta. The responses to B-HT 920 were mediated by α2-adrenoceptors in the vein and by α1-adrenoceptors in the aorta yet concentration-response curves to this agonists were significantly attenuated by diltiazem in both tissues. The results indicate that the resistance of certain α-adrenoceptor-mediated responses in vascular preparations to calcium entry blockers need not be associated with the presence of a significant receptor reserve and that calcium dependency of a response may be determined by the agonist.