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Changes in pituitary response to GnRH during the luteal-follicular transition of the human menstrual cycle
I E Messinis1, D Koutsoyiannis, S Milingos
1Department of Obstetrics and Gynaecology, University of Ioannina, Greece.
Objective:
We studied changes in pituitary response to GnRH during the luteal-follicular transition of the human menstrual cycle.
Design:
Normally cycling women were investigated during two consecutive menstrual cycles. In each woman, GnRH tests were performed during the two LH surges and several times during the luteal-follicular transition. Data for analysis were available in all women on days -8, -6, -4, -2, -1, 1, 2, 3, 4, 5 and 7 in relation to the onset of second menstruation (day 1).
Patients:
Five normally ovulating parous women were studied.
Measurements:
Pituitary response to GnRH was calculated as the net increase in LH and FSH at 30 minutes (delta LH and delta FSH) above the basal value.
Results:
delta LH and delta FSH showed a similar pattern of significant changes during the luteal-follicular transition. They decreased progressively from days -8 to 1 and increased on day 2. delta LH and delta FSH then decreased on days 3 and 4 and showed a further increase on days 5 and 7. In contrast to these changes, basal FSH levels increased from days -2 to 1 and remained high up to day 5, while basal LH levels showed a trend to increase only after the onset of menses.
Conclusions:
These results demonstrate that the increase in basal FSH secretion during the luteal-follicular transition is GnRH independent. It is suggested that LH and FSH release under the stimulation by GnRH is regulated by a common mechanism.