Potentiation of suckling-induced release of prolactin by inhibition of brain catecholamine synthesis.
The effects of a catecholamine synthesis inhibitor, alpha-methyl-p-tyrosine (alpha-MT), on the accumulation of newly synthesized brain catecholamines and plasma prolactin concentration were studied in lactating rats. [3H]tyrosine was administered to rats 10 minutes before decapitation, and the rate of its incorporation into [3H]dopamine and [3H]norepinephrine was measured in whole brain. Injection of alpha-MT (3.15--12.50 mg/kg) via a carotid cannula increased plasma prolactin levels and decreased the accumulation of newly synthesized brain catecholamines in nonsuckled, lactating rats compared to rats injected with .9% saline solution. Mother rats pretreated with saline solution were suckled for 20 minutes by pups which previously were separated from the mother rats for 5 hours. This treatment resulted in significantly increased plasma prolactin levels compared to nonsuckled controls. In rats pretreated with alpha-MT for 20 minutes, suckling resulted in a further increase in plasma prolactin levels which was significantly greater than the increase caused by suckling or alpha-MT alone. These results suggest that inhibition or catecholamine synthesis had a facilitatory effect on the brain mechanisms responsible for prolactin release in response to suckling.
D000818:Animals; D001921:Brain / Q000378:metabolism*; D002395:Catecholamines / Q000096:biosynthesis*; D004298:Dopamine / Q000096:biosynthesis; D005260:Female; D007774:Lactation; D008781:Methyltyrosines / Q000494:pharmacology*; D009638:Norepinephrine / Q000096:biosynthesis; D011247:Pregnancy; D011388:Prolactin / Q000378:metabolism*; D051381:Rats; D013268:Stimulation, Chemical; D014443:Tyrosine / Q000378:metabolism
D002395:Catecholamines; D008781:Methyltyrosines; D014443:Tyrosine; D011388:Prolactin; D004298:Dopamine; D009638:Norepinephrine