Relaxation of isolated guinea pig trachea, bronchi and pulmonary arteries produced by vasoactive intestinal peptide (VIP).

Vasoactive intestinal peptide (VIP) relaxed isolated guinea pig airways contracted with carbamylcholine and isolated pulmonary arteries contracted with prostaglandin F2 alpha. VIP was more potent as a relaxant agonist on trachea than on bronchi but was equipotent on the main and branch pulmonary artery. The VIP-induced relaxation of either airway or artery segments was not altered by pretreatment of animals with reserpine or pretreatment of isolated tissues with propranolol, metiamide, indomethacin or theophylline. These results are consistent with a direct relaxant effect by VIP in guinea pig lung.