Interactions between morphine and the opioid-like peptides in the rat vas deferens.
1 Morphine, methadone, levorphanol, pethidine, etonitazene and related morphine-like alkaloids produced an increase in the electrically-evoked muscular contraction of the rat vas deferens. In contrast, the enkephalins and beta-endorphin caused inhibition of the twitching. 2 The concentration of beta-endorphin required to inhibit by 50% the muscular twitch was about 50 to 100 times less than that of the enkephalins. 3 Pretreatment of the vasa with morphine antagonized the inhibition of the neuromuscular transmission caused by either beta-endorphin or enkephalin. 4 Conversely, pretreatment with beta-endorphin sensitized the vasa to the increase in twitch tension caused by morphine. 5 Morphine did not alter the sensitivity to exogenously administered noradrenaline, dopamine or potassium.
D000818:Animals; D001665:Binding Sites; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D004558:Electric Stimulation; D004723:Endorphins / Q000494:pharmacology*; D004745:Enkephalins / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D009020:Morphine / Q000494:pharmacology*; D009119:Muscle Contraction / Q000187:drug effects; D051381:Rats; D011957:Receptors, Opioid / Q000187:drug effects; D014649:Vas Deferens / Q000187:drug effects*
D004723:Endorphins; D004745:Enkephalins; D011957:Receptors, Opioid; D009020:Morphine