PULSATILE SECRETION OF LH, FSH, PROLACTIN, OESTRADIOL AND PROGESTERONE DURING THE HUMAN MENSTRUAL CYCLE

SUMMARY The pulsatile secretion of gonadotrophins and ovarian steroids was studied in normal women at different stages of the menstrual cycle. The concentration of LH, FSH, Prolactin (PRL), oestradiol and progesterone were measured in samples of plasma collected every 15 min for 6 h and the frequency and amplitude of each episodic pulse of hormone estimated. Although significant fluctuations occurred in the concentration of each hormone, LH showed the most easily identifiable pulses the frequency of which increased significantly from the early follicular to the late follicular phase of the cycle (3.4±0.3 v. 4.4±0.2 pulses 6 h P<0.01). During the luteal phase the basal concentration of LH (5.6±0.9 U/l), pulse amplitude (7.4±1.7 U/l) and frequency (1.6±0.2/6 h) were much lower than at any stage of the follicular phase (P<0.001). The concentration of FSH and PRL showed a similar but less marked change to that of LH throughout the menstrual cycle with a significant decline in both basal concentration and pulse frequency in the luteal phase of the cycle. Although only 47% of all LH pulses were associated with a pulse of FSH, 70% of FSH and prolactin pulses occurred within 15 min of an LH pulse. The basal concentration of oestradiol increased significantly from the early follicular to the late follicular phase of the cycle (P<0.001). There was evidence of episodic secretion of oestradiol with the frequency of pulses declining from a maximum of 4.3±0.6/6 h in the mid‐follicular phase to 1.8±0.5/6 h in the luteal phase (P<0.02). In the follicular phase 74–80% of LH pulses were followed within 100 min by a significant rise in the concentration of oestradiol. It is suggested that: the secretion of LH, FSH, PRL, oestradiol and progesterone is episodic in nature; a significant number of secretory episodes of FSH, LH and PRL are coincidental; the increased secretion of oestradiol from the pre‐ovulatory follicle is associated with a rise in the frequency of episodic pulses of LH.