title: The effects of leucine-enkephalin on the spontaneous motility of the circular muscle of the cat colon.
abstract: Since the effects of endogenously occurring opiates in the regulation of colonic motility are unknown, we set out to study the actions of leucine-enkephalin on the spontaneous contractile and electrical activity of the isolated circular muscle of the cat colon. The muscle strips exhibited regular rhythmic contractions and myoelectrical slow waves 3.67 +/- 0.16 (SEM) times/min. Mean contraction force was 1.20 +/- 0.09 mN. Leucine-enkephalin caused a dose-dependent increase in contractile activity by a factor of 8.24 +/- 2.68; ED50 was 2.23 X 10(-9) M, ED100 4.33 X 10(-8) M. Methionine-enkephalin was equally effective, but morphine was much less effective. Naloxone acted as a specific antagonist. Concentrations of 10(-8) and 10(-7) M shifted the dose-response curve to the right, at the ED50 of leucine-enkephalin by 0.66 and 1.63 log units, respectively. Naloxone exhibited the characteristics of competitive antagonism; pA2 was -8.69, the slope was 1.06. Other antagonists did not affect the enkephalin actions on the muscle. The results of this study suggest that leucine-enkephalin acts on specific receptors of the circular muscle of the cat colon. It is conceivable, therefore, that leucine-enkephalin exerts its effects under physiological conditions to increase segmenting motor activity.
mesh_terms: D000818:Animals; D001285:Atropine / Q000494:pharmacology; D002415:Cats; D004305:Dose-Response Relationship, Drug; D004743:Enkephalin, Leucine / Q000494:pharmacology*; D004744:Enkephalin, Methionine / Q000494:pharmacology; D005260:Female; D066298:In Vitro Techniques; D008297:Male; D009020:Morphine / Q000494:pharmacology; D009119:Muscle Contraction / Q000187:drug effects*; D009130:Muscle, Smooth / Q000502:physiology*; D009270:Naloxone / Q000494:pharmacology; D010646:Phentolamine / Q000494:pharmacology; D011957:Receptors, Opioid / Q000187:drug effects; D013779:Tetrodotoxin / Q000494:pharmacology
chemical_list: D011957:Receptors, Opioid; D009270:Naloxone; D013779:Tetrodotoxin; D004744:Enkephalin, Methionine; D004743:Enkephalin, Leucine; D009020:Morphine; D001285:Atropine; D010646:Phentolamine