title: Effects of morphine and methionine-enkephalin on the smooth muscle tonus and the contraction induced by transmural stimulation in the carp (Cyprinus carpio) intestinal bulb.
abstract: The effects of morphine and methionine-enkephalin (met-enkephalin) on the smooth muscle tonus and the contraction induced by transmural stimulation were investigated in the isolated intestinal bulb of carp in vitro. Morphine (30 nM-3 microM) and met-enkephalin (3 nM-5 microM) caused dose-dependent non-sustained contraction. Naloxone (10 nM) inhibited the contraction induced by morphine or met-enkephalin in a competitive manner. Tetrodotoxin (400 nM) or atropine (500 nM) did not inhibit the contraction induced by morphine or met-enkephalin. Cooling of the bath fluid from 20 to 10 degrees C decreased nicotine- and transmural stimulation-induced contraction. But met-enkephalin-induced contraction was not affected. Transmural stimulation-induced contraction (3 Hz) was not affected by pretreatment with morphine, met-enkephalin or naloxone. The results demonstrated that morphine or met-enkephalin caused contraction of the smooth muscle directly through the activation of opiate receptors on the smooth muscle cells and neither morphine nor met-enkephalin regulated the cholinergic neurotransmission presynaptically.
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D001285:Atropine / Q000494:pharmacology; D002347:Carps; D004155:Diphenhydramine / Q000494:pharmacology; D004558:Electric Stimulation; D004744:Enkephalin, Methionine / Q000494:pharmacology*; D005260:Female; D018738:Hexamethonium; D006584:Hexamethonium Compounds / Q000494:pharmacology; D007422:Intestines / Q000187:drug effects / Q000502:physiology*; D007537:Isometric Contraction / Q000187:drug effects; D008297:Male; D009020:Morphine / Q000494:pharmacology*; D009119:Muscle Contraction / Q000187:drug effects*; D009129:Muscle Tonus / Q000187:drug effects*; D009270:Naloxone / Q000494:pharmacology; D013779:Tetrodotoxin / Q000494:pharmacology
chemical_list: D006584:Hexamethonium Compounds; D009270:Naloxone; D018738:Hexamethonium; D013779:Tetrodotoxin; D004744:Enkephalin, Methionine; D009020:Morphine; D001285:Atropine; D004155:Diphenhydramine; D000109:Acetylcholine