SHORT-TERM REGULATION OF LH AND FSH SECRETION IN CYCLIC WOMEN

The effects of six consecutive LH-RH injections (25 μg intravenously each) at 90 min intervals on serum gonadotrophin and serum ovarian steroid levels were investigated in cyclic women (n= 13) in the follicular, midcycle and luteal phase of the menstrual cycle.The maximum responseof LH pituitary reaction to repeated LH-RH injections was smallest in the follicular phase, higher in the luteal phase and greatest in the midcycle phase of the menstrual cycle. The maximum response of FSH reaction was small both in the follicular and luteal phase and again greatest in the midcycle phase.The pituitary response patternafter six consecutive LH-RH injections also varied throughout the cycle. On the one hand there was a constant pronounced increase in the response from the first to the second LH-RH injection for both LH and FSH, while the second of all six increments (Δ2) was the maximum increment. On the other hand, for both LH and FSH the responses Δ3to Δ6decreased progressively in the luteal phase and showed an even further pronounced decrease in the midcycle phase, indicating an exhaustion of pituitary secretion. In the follicular phase, however, the decrease in the responses Δ3to Δ6for LH was small, but significant. For FSH no significant changes between the responses Δ2to Δ6were observed.Secondary to the elevated gonadotrophin levels, serum levels of oestradiol, 17-hydroxyprogesterone and progesterone increased slightly in the follicular phase and distinctly in the luteal phase of the cycle.Possible mechanisms are discussed which might provide an explanation for the observed augmentation and subsequent diminution of pituitary reaction.