Comparison of the responses of the simian and canine coronary circulations to autonomic drugs.

We studied Japanese monkeys, an anubis baboon, and dogs to determine possible differences in the responsiveness of the simian and the canine coronary vasculature to autonomic drugs. Under ketamine and pentobarbital anesthesia the left anterior descending coronary artery was perfused with autologous blood at constant pressure. All drugs were injected intraarterially. In monkeys, acetylcholine and methacholine produced vasoconstriction followed by vasodilatation, and vasoconstriction was marked after large doses. Both responses were antagonized by atropine. In dogs, the two muscarinic receptor agonists produced only vasodilatation. In the baboon, acetylcholine injected into the femoral artery produced only vasodilatation. These results indicate that vasoconstriction mediated by muscarinic receptors is characteristic of the simian coronary vasculature. In monkeys, norepinephrine produced vasoconstriction followed by vasodilatation. The former response was abolished and the latter enhanced by phentolamine. In dogs, norepinephrine produced only vasodilatation. This response was reduced and preceded by vasoconstriction after atenolol. Methoxamine produced only vasoconstriction, which was weaker in dogs than in monkeys. These results indicate that alpha-adrenoceptors in the coronary vasculature are more important in subhuman primates than in dogs.