Inhibitory effect of progesterone in the postcastration gonadotrophin rise in women

This study was designed to investigate the effects of progesterone on the gonadotrophin rise after bilateral salpingo-oophorectomy (BSO). Twenty-eight regularly menstruating women underwent hysterectomy and BSO during the follicular phase of the menstrual cycle. They were divided into 5 groups depending on the treatment after BSO. Plasma LH and FSH were studied serially for 14 days after BSO and the patterns of LH and FSH rises were contrasted to those observed in the control group which received neither progesterone nor estrogen. LH and FSH levels in the group which were given low dose progesterone only, rose consistently after BSO and these patterns were similar to those seen in the control group. However, the addition of estrogen reduced gonadotrophin rises significantly more than estrogen did alone. Further, the luteal phase level of progesterone solely has a suppressive effect on the gonadotrophin rises after BSO. Our observations suggest that synergism of progesterone with estrogen may exist in suppressing gonadotrophin secretion in the normal luteal phase and should help in understanding why gonadotrophin levels in the luteal phase are lower than those in the follicular phase of the menstrual cycle.