Longitudinal evaluation of the luteal phase and its transition into the follicular phase

The precise patterns of LH, FSH, and PRL secretion and their correlation with estradiol (E2) and progesterone (P) secretion during the entire luteal phase have not been elucidated. To analyze in detail the secretory patterns of these hormones we performed 29 consecutive studies in 5 healthy, regularly menstruating women throughout their luteal phase [days 0 (ovulation), 2, 6, 10, and 14] and subsequent early follicular phase (day 2F). During each study plasma LH, FSH, PRL, E2, and P were measured at 10-min intervals for 6 h. Both plasma LH concentrations and LH pulse frequency declined from days 0 to 10 and increased thereafter, whereas LH pulse amplitude continued to decline throughout the luteal and early follicular phases. Plasma FSH concentrations followed a pattern similar to that of LH; however, there was a larger increase in the FSH level on days 14 and 2F. Plasma PRL levels declined initially on day 2 and again on day 14. Regression analysis indicated a positive correlation between LH concentrations and LH pulse frequency (r = 0.715; P less than 0.001) and between PRL and E2 concentrations (r = 0.528; P less than 0.01). A negative correlation was found between plasma P concentrations and both LH concentrations (r = -0.521; P less than 0.01) and LH pulse frequency (r = -0.633; P less than 0.001) and between plasma E2 and FSH concentrations (r = -0.762; P less than 0.001). Thirty-six (65%) PRL pulses and only 11 (39%) FSH pulses coincided with LH pulses. There was no clear pulsatile pattern of secretion of either E2 or P. We conclude that 1) the plasma LH, FSH, PRL, E2, and P concentrations vary markedly throughout the luteal phase; 2) the plasma LH level is largely dependent on the frequency of LH pulses; 3) plasma P decreases plasma LH by reducing the frequency of LH pulses; 4) the remarkable synchrony between PRL pulses and LH pulses implies that their secretion may be regulated by a common neuroendocrine mechanism; and 5) the preferential increase in FSH during the late luteal phase may play an important role in follicular recruitment for the subsequent cycle.