Pituitary-ovarian interactions during follicular maturation and ovulation.

During the past decade, research on hypothalamic-pituitary-ovarian relationships in ovulation has explored the contributions of ovarian steroids and other possible ovarian-derived endocrine factors, such as inhibin, follistatin, and activin. Follistatin and activin probably have a significant intraovarian and intrapituitary function but are not likely to have critical endocrine roles during the follicular phase. Studies carried out with both recombinant and highly purified forms of follicle-stimulating hormone in humans and monkeys indicate that this hormone is the primary stimulant of follicular growth and development. Studies on animals may have led to incorrect emphasis on the local role of estradiol in primate follicular growth. It appears that estradiol is not a critical folliculotropin in humans, although it may have some important direct effects on the oocyte.