Effect of ACTH on opiate inhibition of oxytocin release.
beta-Endorphin (200ng), dynorphin1-17 (2 micrograms) and morphine (4 micrograms) suppressed the osmotically-evoked release of oxytocin in anaesthetized lactating rats. ACTH1-24 (0.2-3 micrograms) administered intraventricularly 3 min before beta-endorphin or morphine attenuated their inhibitory action, but when applied afterwards was never seen to reverse their effects although this was achieved with naloxone (lmg X kg-1, i.v.). ACTH however, was ineffective against dynorphin. At higher doses an opiate-like action of ACTH was observed. Thus ACTH may act as a partial antagonist and at higher doses as a partial agonist of the opiate receptor for which it is known to have an affinity. It is suggested that suppression of oxytocin release by endogenous beta-endorphin could be modified by ACTH with which it may be co-released.
D000324:Adrenocorticotropic Hormone / Q000031:analogs & derivatives*; D000818:Animals; D003366:Cosyntropin / Q000494:pharmacology*; D004399:Dynorphins; D004723:Endorphins / Q000494:pharmacology*; D005260:Female; D007774:Lactation / Q000187:drug effects; D009020:Morphine / Q000494:pharmacology*; D010121:Oxytocin / Q000378:metabolism*; D010446:Peptide Fragments / Q000494:pharmacology*; D011247:Pregnancy; D011433:Propranolol / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains
D004723:Endorphins; D010446:Peptide Fragments; D003366:Cosyntropin; D010121:Oxytocin; D004399:Dynorphins; D009020:Morphine; D000324:Adrenocorticotropic Hormone; D011433:Propranolol