Reactivity and contractility of rat main pulmonary artery to vasoactive agents.

In vitro studies were undertaken to determine the reactivity and contractility of the rat main pulmonary artery (RPA) to some selected vasoactive agents. Oxytocin was found to be inactive RPA exhibited a poor responsiveness to vasopressin, acetylcholine, histamine, and bradykinin. Prostaglandins B2 and E2, K+, angiotensin, sympathomimetic agents (epinephrine and isoproterenol), 5-hydroxytryptamine (5-HT), and [Ca2+]0 were found to produce, consistently, potent and concentration-related contractions of the RPA. Pulmonary arterial strips that were precontracted with 5-HT responded with relaxations to isoproterenol in low concentrations and with contractions in high concentrations. Blockade of isoproterenol-induced relaxation by propranolol provides evidence for the existence of specific beta-adrenoceptors in RPA. The selective antagonism of contractile responses induced by epinephrine, 5-HT, acetylcholine, and histamine by phentolamine, methysergide, atropine, and pyrilamine, respectively, provides evidence for the occurrence of specific alpha-adrenergic, "D"-serotonin as well as some cholinergic (muscarinic) and H1-histamine receptors in the RPA.