The corpus luteum: determinants of progesterone secretion in the normal menstrual cycle

Fourteen normal volunteers were studied during one menstrual cycle. Follicular development, the luteinizing hormone (LH) surge, and the relationship between LH and progesterone secretion in the luteal phase were studied to determine the factors that control corpus luteum function. Follicular development was assessed by measuring follicle size and daily estradiol (E2) levels; the LH surge was quantified by determining the area under the curve. Although there was a significant positive correlation between mean follicle diameter and E2, these same parameters did not correlate with postovulatory progesterone secretion; nor did the LH surge correlate with progesterone secretion. A decrease in LH pulse frequency occurred in moving from the follicular to the luteal phase. There was a trend toward an increase in the late luteal LH pulse frequency compared with the midluteal phase, but this was not significant. Progesterone was secreted in an intermittent (pulsatile) fashion in the midluteal and late luteal phases. The general decrease in progesterone in the latter days of the menstrual cycle appears to be due to a decrease in the progesterone pulse amplitude. A significant correlation between LH and progesterone was present when the data were "smoothed"; however, there was not a significant synchrony for LH and progesterone pulses for most of the subjects when the initial data were analyzed by objective criteria. Progesterone secretion in the luteal phase is quite complex and leads to highly variable serum levels of progesterone when samples are obtained at random from normal women.