title: Comparison of the biological activity of canine and porcine motilin in rabbit.
abstract: The biological activity of porcine and canine motilin was studied in rabbits by establishing dose-response curves of both peptides using two different methods. The dissociation constant, obtained from the displacement of iodinated porcine motilin by canine motilin was 0.6 +/- 0.3 nM, versus 1.2 +/- 0.4 nM for porcine motilin. For the 13-norleucine and 13-leucine analogues of porcine motilin a value of 0.8 +/- 0.3 nM was obtained. Both motilins were almost equipotent in stimulating the in vitro contractile response of longitudinal smooth muscle strips: half-maximal effect was achieved at a concentration of 1.0 +/- 0.1 nM for canine versus 1.3 +/- 0.2 nM for the 13-norleucine analogue of porcine motilin. We conclude that porcine and canine motilin have a comparable bioactivity in the rabbit, although canine motilin is slightly more effective. The motilin receptor is probably specific for the N-terminal portion which is identical in both molecules.
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D004285:Dogs; D004305:Dose-Response Relationship, Drug; D004386:Duodenum / Q000378:metabolism / Q000502:physiology; D066298:In Vitro Techniques; D009037:Motilin / Q000378:metabolism / Q000494:pharmacology*; D009119:Muscle Contraction / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D051381:Rats; D011964:Receptors, Gastrointestinal Hormone / Q000378:metabolism; D018013:Receptors, Neuropeptide; D013045:Species Specificity; D013552:Swine
chemical_list: D011964:Receptors, Gastrointestinal Hormone; D018013:Receptors, Neuropeptide; C050802:motilin receptor; D009037:Motilin; D000109:Acetylcholine