Effect of peptide with histidine and isoleucine amide on isolated circular muscle of portal vein of guinea pig

Effect of peptide with histidine and isoleucine amide on isolated circular muscle of portal vein of guinea pig Xiang WEI%Wen-Hsiung LEE%Zao-chen YANG%Haruaki YAJIMA A synthetic porcine peptide with NH-terminal histidine and isoleucine amide (PHI) was found to decrease tensive increment of isolated circular muscle of guinea pig portal vein induced by methoxamine(4 microM) at concentrations of 0.067-2.2 microM.The effect of PHI(pD2=6.0) was similar(P>0.05) to that of isoprenaline(pD2=6.4). The action of PHI was not affected by propranolol(6.8 microM) and atropine(1.4 microM), but antagonized by vasoactive intestinal polypeptide(VIP) antiserum. These results suggest that the effect of PHI on the tension of the circular muscle to guinea pig portal vein is not related to adrenoceptors and cholinoceptors but probably to VIP receptors.