The influence of cholinergic, adrenergic, and serotonergic drugs on the afternoon surge of plasma prolactin in ovariectomized, estrogen-treated rats.
The effects of systemic administration of cholinergic, adrenergic, and serotonergic drugs on the afternoon surge of plasma prolactin was investigated using ovariectomized, polyestradiol phosphate (PEP)-injected rats bearing aortic catheters. Basal prolactin levels were elevated and similar after PEP administration for a period of 5 weeks, and an afternoon surge in plasma prolactin persisted for a period of 3 weeks before the magnitude of the surge diminished. The plasma estradiol levels were significantly higher for the 1100 and 1300 h samples than for the 1500 and 1700 h samples. Cornified vaginal epithelia were predominant in the vaginal smears of all animals throughout the 49-day experimental period. The cholinergic agonists arecoline, nicotine, and carbachol significantly inhibited the afternoon surge of prolactin. The muscarinic antagonist atropine resulted in a partial inhibition of the surge while the nicotinic antagonist mecamylamine did not have any inhibitory effect. The alpha-adrenergic blockers phenoxybenzamine and phentolamine and the beta-blocker propranolol inhibited the prolactin surge, with phenoxybenzamine being most effective. The administration of the serotonergic antagonist methysergide resulted in only a partial blockade of the afternoon prolactin surge. The data suggest that both the adrenergic and serotonergic systems may have a positive input in the afternoon surge of plasma prolactin. It appears that the cholinergic system does not play a significant role in the afternoon surge.
D000818:Animals; D001115:Arecoline / Q000494:pharmacology; D001285:Atropine / Q000494:pharmacology; D002217:Carbachol / Q000494:pharmacology; D002369:Castration; D002940:Circadian Rhythm; D004958:Estradiol / Q000502:physiology*; D005260:Female; D008784:Methysergide / Q000031:analogs & derivatives / Q000494:pharmacology; D009538:Nicotine / Q000494:pharmacology; D010277:Parasympathomimetics / Q000494:pharmacology*; D010643:Phenoxybenzamine / Q000494:pharmacology; D010646:Phentolamine / Q000494:pharmacology; D011388:Prolactin / Q000097:blood*; D011433:Propranolol / Q000494:pharmacology; D051381:Rats; D013566:Sympathomimetics / Q000494:pharmacology*; D013997:Time Factors
D010277:Parasympathomimetics; D013566:Sympathomimetics; D010643:Phenoxybenzamine; D001115:Arecoline; D004958:Estradiol; D009538:Nicotine; D001285:Atropine; D002217:Carbachol; D011388:Prolactin; D011433:Propranolol; D008784:Methysergide; D010646:Phentolamine