Responses of pulmonary vasculature of cattle to dopamine and apomorphine

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Abstract
Both dopamine and apomorphine caused concentration-dependent contractions of the bovine pulmonary artery from rest. Both of these compounds caused relaxation of histamine-precontracted arterial and venous strips after .alpha.-adrenoceptor blockade. Arterial contraction elicited by dopamine was inhibited either by phentolamine (.alpha.-blocker) or by the dopamine-selective antagonists, spiperone and butaclamol. Apomorphine in the highest concentration (> 10-5 M) inhibited dopamine-induced contractions. Dopamine- and apomorphine-induced vascular relaxations were attenuated by propranolol but not by spiperone or butaclamol. Evidently, dopamine- and apomorphine-induced relaxation in these preparations is most likely mediated through .beta.-adrenergic mechanisms, whereas dopamine-induced contractions seem to involve both .alpha.-adrenergic and dopaminergic receptors.

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