Responsiveness of isolated monkey coronary arteries contracted with alpha 1- and alpha 2-adrenoceptor agonists to diltiazem.

Diltiazem induced a concentration-dependent relaxation of monkey coronary arterial strips which were partially contracted with clonidine, phenylephrine, norepinephrine, prostaglandin F2 alpha. This relaxation occurred to a similar extent, but was significantly less than that observed in arteries contracted with K+. Contractions mediated via alpha 2-adrenoceptors do not appear to be more susceptible to diltiazem than those caused by activation of alpha 1-adrenoceptors and prostaglandin F2 alpha receptors.