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  • Title: Does the hypothalamic tyrosine-hydroxylase inhibition mediate the positive feedback of progesterone on gonadotropin release in women?
    Author: Nicoletti I, Filipponi P, Fedeli L, Sfrappini M, Santeusanio F, Brunetti P.
    Journal: Horm Metab Res; 1984 Mar; 16(3):136-9. PubMed ID: 6143717.
    Abstract:
    Neuropharmacological studies suggest a common inhibitory role for the hypothalamic dopaminergic pathway on gonadotropin and prolactin pituitary release, in humans. As a consequence, it has been hypothesized that the inhibition of hypothalamic tyrosine-hydroxylase and the subsequent fall in dopamine synthesis is involved in the positive feedback of progesterone on LH and PRL pituitary release in estrogen-primed hypogonadal women. The aim of our study was to verify whether an inhibition of tyrosine-hydroxylase may really account for the progesterone action on gonadotropin and prolactin secretion. For this purpose, we compared the effect of a specific tyrosine-hydroxylase inhibitor (alpha-methyl-p-tyrosine, AMPT) with the effect of progesterone on gonadotropin and prolactin release in estrogen-primed postmenopausal women. Progesterone induced a marked release of LH (delta: 129.7 +/- 16.5 mlU/ml, mean +/- SE) and a slight increase in FSH (delta: 39.4 +/- 11.6 mlU/ml) and PRL (delta: 15.3 +/- 2.8 ng/ml) serum levels. Acute or two-day administration of AMPT was followed by a marked rise in PRL serum levels (delta: 82.9 +/- 13.8 and 88.3 +/- 8.2 ng/ml, respectively) while there were no significant increases in serum LH (delta: 5.4 +/- 2.6 and 3.3 +/- 4.6 mlU/ml) and FSH (delta: 3.4 +/- 0.9 and -0.4 +/- 2.9) concentrations. The ineffectiveness of a specific tyrosine-hydroxylase inhibitor in simulating the progesterone effect on gonadotropin secretion seems to negate the hypothesis that a reduction in hypothalamic dopaminergic activity mediates the positive feedback of progesterone on gonadotropin release.
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