Circulating prolactin levels during the menstrual cycle: Episodic release and diurnal variation

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Abstract

Assessment of temporal relationship between levels of prolactin (PRL), gonadotropins, and ovarian steroids in 14 ovulatory cycles was made. Serum PRL concentrations were determined by a homologous radioimmunoassay. Our data showed that, although the highest mean PRL concentration was found on the day of LH-surge and the day after estrogen peak, a consistent pattern of circulating PRL in daily morning samples was not present in ovulatory cycles; variations in random fluctuation with erratic spikes were observed within cycles and between subjects. In two cycles studied, despite markedly elevated PRL levels (eightfold) induced by amphetamine, optimal ovulatory events occurred in terms of both hormonal patterns and luteal function. These findings implicate a lack of apparent physiologic role of PRL in the regulation of ovarian function in human subjects. The random daily fluctuation of PRL was further characterized in samples obtained at 10 to 30 minute intervals during different days of five ovulatory cycles and continuous sampling during day and night was made in three of five studies; a clear episodic nature of PRL release was disclosed. A circadian rhythm with marked elevation during sleep which was composed of multiple peaks with larger excursions than those found during waking periods was revealed. The event of sleep-induced PRL rise was initiated shortly (30 to 90 minutes) after the onset of sleep and ceased upon wakening. In one subject a quantitatively greater nocturnal PRL release around midcycle (eightfold) than during the follicular and the luteal phases (threefold) was found. These data would facilitate future elucidation of the inapparent role as well as the neuroendocrine regulation of PRL secretion during the human menstrual cycle.

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    Supported in part by a grant from the Rockefeller Foundation (RF 70029).

    Drs. Ehara and VandenBerg are Rockefeller Foundation Research Fellows in Reproductive Endocrinology.

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