Relaxant effects of vasoactive intestinal peptide and bethanechol in cat intrapulmonary artery

The relaxant actions of vasoactive intestinal peptide (VIP) and bethanechol were examined on ring segments of intrapulmonary artery (IPA) isolated from cat lung. On a molar basis, VIP was 75 times more potent than bethanechol; however, VIP was less efficacious than bethanechol in reversing phenylephrine induced tone. Responses to VIP were unaffected by pretreatment of the tissues with atropine, indomethacin or avian pancreatic polypeptide. These results suggest that VIP may participate in the regulation of pulmonary vascular smooth muscle tone through a potent relaxant action that occurs independent of muscarinic cholinergic receptor activation or liberation of prostaglandins.