FIGURE 2.
Endocrine profiles of estradiol (E2), LH, FSH, and progesterone (P) during the ovarian cycle in the cynomolgus monkey and presumed feedback actions of ovarian hormones. The day of ovulation is denoted as zero, and days for follicular and luteal phases are counted relative to ovulation time point. Endocrine data represent M ± SD of forty-four animals except for FSH with data from fourteen animals. During ovulation, ovarian steroids are assumed to exert primarily a direct and positive feedback effect on pituitary gonadotropin secretion, whereas negative feedback actions occur during the follicular and luteal phases. Studies in ovariectomized monkeys also suggested a hypothalamic site of E2 action. Whether progesterone also has a direct positive effect on hypothalamus is unclear.