title: Morphine, beta-endorphin and [D-Ala2] Met-enkephalin inhibit oxytocin release by acetylcholine and suckling.
abstract: Morphine inhibits suckling-induced oxytocin (OT) release in lactating mice. Since beta-endorphin and enkephalins have several actions in common with morphine, the action of these opioid peptides on OT release was investigated. In anesthetized lactating rats, OT release was achieved by intraventricular injection of acetylcholine (ACh) or by the physiological stimulus of suckling. The amount of OT released was estimated by comparing milk-ejection responses to these stimuli to those following known amounts of intravenous (IV) OT. Both beta-endorphin and [D-Ala2]Met-enkephalin inhibited ACh-induced and suckling-induced OT release. Naloxone antagonized opiate inhibition in both cases.
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D004723:Endorphins / Q000494:pharmacology*; D004744:Enkephalin, Methionine / Q000031:analogs & derivatives* / Q000494:pharmacology; D005260:Female; D007774:Lactation / Q000187:drug effects*; D009020:Morphine / Q000494:pharmacology*; D010121:Oxytocin / Q000037:antagonists & inhibitors* / Q000378:metabolism; D011247:Pregnancy; D051381:Rats; D001615:beta-Endorphin
chemical_list: D004723:Endorphins; D010121:Oxytocin; D004744:Enkephalin, Methionine; D001615:beta-Endorphin; C013801:enkephalin-Met, Ala(2)-; D009020:Morphine; D000109:Acetylcholine