Influence of preovulatory estradiol concentration on diurnal and pulsatile prolactin secretion patterns.

We evaluated the effect of preovulatory concentrations of estradiol on the 24-hour profile of prolactin secretion in women with regular menstrual cycles. An estradiol preparation was chosen to allow comparison with physiologic events. Estradiol benzoate, 1 mg intramuscularly, was administered for 7 days to achieve estradiol concentrations just above preovulatory levels (424 +/- 54 pg/ml); 24-hour mean prolactin concentrations increased threefold (14.0 +/- 2.1 to 40.6 +/- 7.1 ng/ml). Prolactin pulse frequency increased significantly (p less than 0.001) during waking hours after estradiol benzoate administration. The diurnal pattern of prolactin secretion was maintained with estradiol benzoate, although the sleep acrophase often reached high concentrations (86 +/- 11 ng/ml). These results suggest in women with regular menstrual cycles: (1) that estrogen administration that achieves slightly greater than preovulatory estradiol concentrations can stimulate prolactin release, (2) that estradiol may elevate prolactin by increasing its pulsatile secretion, (3) that estradiol does not alter the diurnal pattern of prolactin secretion, (4) that estradiol concentrations just above preovulatory levels can be associated with markedly elevated prolactin concentrations.