Tryptamine receptors in rat pulmonary artery.

Tryptamine and 5-hydroxytryptamine (5-HT) are equipotent in contracting spiral strips of rat isolated pulmonary artery, in doses between 5 and 20 mug. These 5-HT receptors are blocked by low concentrations (c. 10(-9) M) of both methysergide and morphine. In rat isolated lung perfused via the pulmonary circulation, 5-HT caused increases in perfusion pressure which were also antagonized by methysergide and by morphine. These vascular 5-HT receptors cannot therefore be classified as M or D receptors and, furthermore, are different from those 5-HT receptors mediating release of spasmogens from rat isolated lungs.