[Phenoxybenzamine antagonism of ergometrine-induced increase of coronary artery resistance in rabbits].

Ergometrine is currently used as a test for Prinzmetal variant angina, causing specifically a coronary artery spasm in these patients, even if the mechanism of this drug on coronaries is still unclear. In isolated rabbit heart perfused at constant flow the administration of ergometrine at the concentration of 2.2 x 10(-5) M evoked a marked and longlasting increase of coronary resistance which was revealed by a rise in perfusion pressure from 68.2 +/- 12.9 to 124.4 +/- 21.7 (m +/- SD; n=21). This increase appears only with repeated perfusions of the drug and moreover it was not reproducible in the same preparation after its maximal response. The vasoconstriction was not significantly affected either by atropine or mepyramine, but it was strongly reduced by the phenoxybenzamine pretreatment (2.9 x 10(-6) M; n=8). It is evident the role of alpha-adrenergic receptors in ergometrine effect, but our results do not allow to understand its true mechanism, in fact the noradrenaline release can not be completely excluded.