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Prolactin Pulsatile Characteristics in Postmenopausal Women¹

Neuroendocrine Unit (L.K., V.C.S., A.K.), Department of Neurology (P.N.R.), and the General Clinical Research Center, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts 02114

Address all correspondence and requests for reprints to: Laurence Katznelson, M.D., Neuroendocrine Unit, Massachusetts General Hospital, 55 Fruit Street, BUL457B, Boston, Massachusetts 02114-2696. E-mail: katznelsonl{at}a1.mgh.harvard.edu

Pulsatile PRL secretion undergoes diurnal variation, with maximal PRL release in the evening during sleep in both women and men. However, the impact of the menopause on PRL pulsatile dynamics are largely unknown. To characterize diurnal PRL pulsatile secretion in postmenopausal women, we performed frequent venous sampling over 24 h every 10 min for serum PRL in 7 postmenopausal women (age, 56 ± 4 yr) and in 2 control groups, 8 men (age, 25 ± 8 yr) and 22 cycling women (age, 28 ± 5 yr), at 3 phases of the menstrual cycle. Standard TRH tests (200 µg, iv) were administered at 0900 h after completion of the 24-h sampling, and PRL levels were then obtained at 0, 10, 20, 30, and 60 min in all subjects. PRL pulse characteristics were similar between the postmenopausal women and men. Mean serum PRL levels and PRL pulse frequency were significantly higher in the cycling women than in either postmenopausal women or men over 24 h and during either the day or night periods. Mean serum PRL levels and pulse frequency were significantly higher during the night compared to those during the day in all groups. Pulse amplitude was higher during the night vs. the day in all groups and was highest in the cycling women. PRL responses to TRH administration were greatest in cycling women. These data demonstrate that PRL pulse dynamics are significantly different between postmenopausal women and cycling women, and endogenous estrogen levels may have an important role in this difference. Pulsatile PRL secretion is similar between postmenopausal women and men, suggesting that estrogen levels modulate PRL dynamics across genders.

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