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 and serotonin in the rat. Thirty minutes after its administration iodotyrosine (50 mg/kg) caused a highly significant (P less than 0.0005) rise in serum prolactin and a highly significant (P less than 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 less than 0.05) and median eminence (P less than 0.0025) concentrations of noradrenaline after iodotyrosine administration. Serotonin concentration was significantly reduced (P less than 0.025) in the median eminence but not in the hypothalamus after iodotyrosine administration. These findings suggest that iodotyrosine exerts its prolactin stimulating effect by blockage of dopamine synthesis rather than by receptor blockade.
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Smythe et al. (1979) studied this question.