A Simple Procedure for the Assay of Brain Biogenic Amines by Selected-Ion Monitoring: Its Application to the Elucidation of the Mechanism of Prolactin Release Induced by 3-Iodo-L-Tyrosine
A simple method for the assay of brain biogenic amines by selected-ion monitoring was applied to examination of the effects of 3-iodo-L-tyrosine on the hypothalamic-median eminence concentrations of dopamine, noradrenaline [norepinephrine, NE] and serotonin in the rat. Thirty minutes after its administration iodotyrosine (50 mg/kg) caused a highly significant (P < 0.0005) rise in serum prolactin and a highly significant (P < 0.0025) fall in the concentration of dopamine in the hypothalamus and median eminence where the levels reached 50% of control levels. Less marked but significant falls were also observed in the hypothalamic (P < 0.05) and median eminence (P < 0.0025) concentrations of NE after iodotyrosine administration. Serotonin concentration was significantly reduced (P < 0.025) in the median eminence but not in the hypothalamus after iodotyrosine administration. Idotyrosine exerts its prolactin stimulating effect by blockage of dopamine synthesis rather than by receptor blockade.