The source of pulsatile secretion of progesterone during the human follicular phase

This study was designed to establish the normal pattern of serum progesterone and the origin of its secretion during the follicular phase of the normal menstrual cycle. In the first study, 12 normal women were studied on 3 occasions each at different times during a single follicular phase. Serum samples were collected every 10 min over 8 h, for 6 h before and 2 h after an injection of naloxone (5 mg iv). The mean serum progesterone remained constant (0.9 nmol/L) across the follicular phase until just before ovulation; individual subjects showed pulsatility of progesterone (1-6 pulses/6 h) but there was no relationship of this to LH pulsatility and no variation of progesterone pulsatility across the follicular phase. Naloxone caused an increase in the mean serum progesterone in the early follicular phase to 1.9 +/- 0.7 nmol/L and in the mid and late follicular phase to 2.1 +/- 0.7 nmol/L and 3.4 +/- 2.5 nmol/L, respectively. The second study was performed to assess the contribution of the residual corpus luteum and the developing follicle to the pulsatile secretion of progesterone. Seven anovulatory women with low levels of serum LH and absent LH pulsatility were studied before and after clomiphene (100 mg/day for 5 days) by collecting blood samples every 15 min for 6 h before GnRH (10 mg iv) and for 2 h afterwards. The anovulatory women had comparable mean serum concentration of progesterone (0.9 +/- 0.5 nmol/L) to normal women and similar frequency of progesterone pulsatility (2.1 +/- 1.1 pulses/6 h). After administration of clomiphene, there was no significant change in progesterone pulsatility (1.7 +/- 1.0 pulses/6 h) despite a substantial increase in LH pulsatility (from none to 3.0 +/- 1.0 pulses/6 h). There was no significant increase in serum progesterone after clomiphene or GnRH which both caused a substantial increase in serum LH. The third study involved eight normal women studied before and after treatment with dexamethasone (2 mg/day for 2 days) to assess the adrenal component of progesterone secretion. Blood samples were collected every 10 min for 6 h before and 2 h after naloxone (5 mg iv). Dexamethasone reduced serum progesterone to below assay sensitivity (less than 0.2 nmol/L) and obliterated progesterone pulsatility. The increase in serum progesterone and cortisol induced by naloxone was blocked by dexamethasone; the naloxone-induced rise of serum LH was not affected by dexamethasone. We conclude that neither the preceding corpus luteum nor the developing follicle are important contributors to the serum concentration of progesterone during the normal follicular phase.(ABSTRACT TRUNCATED AT 400 WORDS)