PT - JOURNAL ARTICLE AU - H Takanashi AU - K Yogo AU - K Ozaki AU - M Ikuta AU - M Akima AU - H Koga AU - H Nabata TI - GM-109: a novel, selective motilin receptor antagonist in the smooth muscle of the rabbit small intestine. DP - 1995 May 01 TA - Journal of Pharmacology and Experimental Therapeutics PG - 624--628 VI - 273 IP - 2 4099 - http://jpet.aspetjournals.org/content/273/2/624.short 4100 - http://jpet.aspetjournals.org/content/273/2/624.full SO - J Pharmacol Exp Ther1995 May 01; 273 AB - The pharmacological properties of the cyclic peptide Phe-cyclo[Lys-Tyr(3-tBu)-beta Ala-].trifluoroacetate (GM-109), a selective motilin antagonist, were investigated in the smooth muscle of the rabbit small intestine. GM-109 (0.1-3 microM) competitively inhibited contractions induced by porcine motilin (pMTL) in rabbit isolated duodenum longitudinal strips, with a pA2 value of 7.37 +/- 0.24. However, the contractile response to acetylcholine, to substance P, to prostaglandin F2 alpha and to KCl was unaffected by 10 microM GM-109 in the same preparation. Both GM-109 and pMTL competitively inhibited 125I-pMTL binding to motilin receptors in a homogenate of the rabbit small intestinal smooth muscle tissue. The pKi value of GM-109 and the pKd value of unlabeled pMTL were 7.99 +/- 0.04 and 9.25 +/- 0.06 (each n = 5), respectively. These results indicate that GM-109 is a selective and competitive motilin receptor antagonist in the smooth muscle of the rabbit small intestine. Thus this compound may be a useful pharmacological tool for examining the functional role(s) of motilin.