Responses of pulmonary vasculature of cattle to dopamine and apomorphine

Both dopamine and apomorphine caused concentration-dependent contractions of the bovine pulmonary artery from rest. Both of these compounds caused 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 (greater than 10(-5) M) inhibited dopamine-induced contractions. Dopamine- and apomorphine-induced vascular relaxations were attenuated by propranolol but not by spiperone or butaclamol. These data suggest that 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.