Effect of alpha-melanocyte-stimulating hormone on basal and stimulated release of prolactin: evidence for dopaminergic mediation.
The effects of alpha-melanocyte-stimulating hormone (alpha-MSH) on basal and stimulated of prolactin were studied. Intraventricular (i.v.t.) injection of 2 microgram of alpha-MSH in ovariectomized (OVX) rats produced a 50% depression of plasma prolactin levels within 10 min, whereas 100 ng of alpha-MSH or saline had no effect. 2 microgram of alpha-MSH (i.v.t.) produced a more dramatic and sustained depression of prolactin levels if initial prolactin concentrations were elevated. This dose of alpha-MSH was also effective in lowering plasma prolactin levels in OVX rats, primed 72 h earlier with 50 microgram of estradiol benzoate (s.c.), although this depression was of lower relative magnitude than in the unprimed OVX animals. The intravenous injection of a dopamine receptor blocker, spiroperidol (0.1 mg/kg), prior to (i.v.t.) alpha-MSH blocked the inhibitory effect of alpha-MSH on prolactin release. In vitro, alpha-MSH in doses ranging from 0.5 to 5 microgram did not alter prolactin release from hemipituitaries of male or OVX female rates and from dispersed pituitary cells from female rats. These results suggest that alpha-MSH can modulate prolactin release possibly via the hypothalamic dopaminergic system, and that this modulation may be of greater significance during stress.
D000818:Animals; D002369:Castration; D004298:Dopamine / Q000502:physiology*; D005260:Female; D007700:Kinetics; D008297:Male; D009074:Melanocyte-Stimulating Hormones / Q000494:pharmacology*; D010903:Pituitary Gland, Anterior / Q000187:drug effects / Q000378:metabolism*; D011388:Prolactin / Q000097:blood / Q000378:metabolism*; D011863:Radioimmunoassay; D051381:Rats; D011919:Rats, Inbred Strains; D013134:Spiperone / Q000494:pharmacology
D013134:Spiperone; D011388:Prolactin; D009074:Melanocyte-Stimulating Hormones; D004298:Dopamine