Tryptaminergic receptors in the bovine pulmonary vasculature: effects of ketanserin.

The vasoconstrictor actions of 5-hydroxytryptamine (5-HT) were investigated in the isolated helical strips of the pulmonary artery and vein of the adult bovine and calf. Agonist-antagonist interactions were studied by pretreating the vessels with methysergide, ketanserin and phentolamine and then establishing the dose-response curves to 5-HT or noradrenaline (NA). Methysergide significantly (p less than 0.05) inhibited 5-HT-induced contractions in the vessels. Ketanserin antagonized the vasoconstrictor actions of 5-HT but inhibition was not dose-related. NA-induced contractions of the vessels from the adult bovine were non-competitively inhibited by ketanserin. Phentolamine (PH) competitively antagonized contractions induced by 5-HT and NE in the tissues. The results suggest that 1. ketanserin is a potent, competitive antagonist of 5-HT but a weak antagonist of NE and 2. 5-HT-induced contractions in the bovine pulmonary vessels are mediated via specific tryptamine receptors (5-HT2) and alpha-adrenergic receptors.