Assessment of pituitary secretory capacity in women with hypogonadotrophic hypogonadism by using a long-acting synthetic analogue of luteinizing hormone releasing factor

Pulsatile release of LH and oestradiol during the periovulatory period in women

Blood was collected every 8 h in five women from Day 10 of the menstrual cycle for 5-7 d for the measurement of LH, oestradiol and progesterone. In all women the LH surge started between 2400 and 0800 h before there was any significant decline in the concentration of oestradiol. In order to investigate the pulsatile secretion of LH and estradiol during the mid-cycle surge, blood samples were collected every 5 min for up to 5 h. Immediately before and during the LH surge there were numerous episodic pulses of LH with an interpulse interval (44 +/- 7 min) very similar to that observed in two women with hypergonadotrophic hypogonadism (48 min). The concentration of oestradiol fluctuated in a similar manner although it was not always possible to relate each pulse of oestradiol to a corresponding pulse of LH. The mid-cycle surge of LH is characterized by frequent pulses of high amplitude. These results are compatible with the view that the positive feedback effect of oestradiol is due not only to enhanced sensitivity of the anterior pituitary to LHRH but also to the high frequency of LHRH pulses released from the hypothalamus.

Changes in plasma levels of prolactin, in relation to those of FSH, oestradiol, androstenedione and progesterone around the preovulatory surge of LH in women

Plasma samples were obtained at 8 hourly intervals around the preovulatory surge of LH in three 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 hours 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 hours 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 oestradiol, 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; oestradiol levels did not rise around this time, and declined by 24 h after the onset of the LH surge. These results suggest that (1) the pre-ovulatory LH surge begins between midnight and 0800 h in the majority of women, (2) luteinization of the granulosa cells within the pre-ovulatory follicle occurs in response to the LH surge, (3) the increase in prolactin at the time of the LH surge is not directly related to increasing levels of oestradiol 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.