CHANGES IN PLASMA LEVELS OF PROLACTIN, IN RELATION TO THOSE OF FSH, OESTRADIOL, ANDROSTENEDIONE AND PROGESTERONE AROUND THE PREOVULATORY SURGE OF LH IN WOMEN

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Abstract
Plasma samples were obtained at 8-h intervals around the preovulatory surge of LH [luteinizing hormone] in 3 groups of women with spontaneously ovulatory menstrual cycles, in order to clarify the hormonal events around the time of ovulation. In 21 of 25 women in whom samples were collected every 8 h the start of the LH surge occurred between midnight and 0800. In 16 of these women the concentration of LH, FSH and progesterone was measured every 8 h around the pre-ovulatory surge of LH. A progressive increase in progesterone started with the onset of the LH surge, with a transient fall after 32-40 h at a time coincident with that of ovulation. In 10 women estradiol, androstenedione and prolactin were measured 8-hourly around the pre-ovulatory surge of LH beginning at 0800 h. Prolactin showed a sustained increase in levels beginning at the start of and lasting for the duration of the pre-ovulatory LH surge; estradiol levels did not rise around this time, and declined by 24 h after the onset of the LH surge. The pre-ovulatory LH surge apparently begins between midnight and 0800 in the majority of women. Luteinization of the granulosa cells within the pre-ovulatory follicle evidently occurs in response to the LH surge. The increase in prolactin at the time of the LH surge evidently is not directly related to increasing levels of estradiol but may be due to a decrease in hypothalamic inhibition of prolactin secretion which occurs coincident with the release of LHRH associated with the preovulatory LH surge.

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