Contractile effects of 5-hydroxytryptamine in isolated intrapulmonary arteries and veins

The contractile effects of serotonin (5-hydroxytryptamine, 5-HT) were compared in helical strips of intrapulmonary artery (IPA) and vein (IPV) isolated from lungs of dog, rabbit, cow, and man. 5-HT (10(-8) - 10(-4) M) increased force generation by IPA and IPV from the four species in a concentration-related manner. Sensitivities to 5-HT of IPA and IPV from the four species were similar, with median effective concentrations ranging from 3 X 10(-8) to 3 X 10(-7) M. However, maximal and contractile responses to 5-HT relative to those elicited by potassium were greater in canine and human IPA and bovine IPA and IPV than in rabbit IPA and IPV and canine and human IPV. Results obtained using specific pharmacology blocking agents suggest that 5-HT-induced contraction of canine and rabbit intrapulmonary vessels does not involve alpha-adrenergic mechanisms except, possibly, in rabbit IPV. The contractile effects of 5-HT observed in the present study suggest that 5-HT released from platelets could contribute to increased vascular resistance during pulmonary thromboembolism by actively constricting arterial and venous segments of the pulmonary vascular bed in a variety of species, including man.