Differential inhibitory action by morphine on the release of oxytocin and vasopressin from the isolated neural lobe.
Simultaneous release of both oxytocin and vasopressin was evoked by electrically stimulating the isolated neural lobe. Morphine inhibited the electrically evoked release of both oxytocin and vasopressin, but whereas the opiate antagonist naloxone reversed the suppression of oxytocin release it was without effect against the opiate block of vasopressin secretion. Thus, although the secretion of both neurohypophysial hormones can be suppressed by opiates, the mechanisms may involve different types of receptors. We also provide evidence that, at least for the oxytocin neurones, the presence of endogenous opioid peptides in the neural lobe limits the amount of hormone released by electrical stimulation.
D000818:Animals; D004558:Electric Stimulation; D009020:Morphine / Q000494:pharmacology*; D010121:Oxytocin / Q000037:antagonists & inhibitors / Q000378:metabolism; D010902:Pituitary Gland / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D014667:Vasopressins / Q000037:antagonists & inhibitors / Q000378:metabolism
D014667:Vasopressins; D010121:Oxytocin; D009020:Morphine