Feedback effect of estradiol on follicle-stimulating hormone and prolactin secretion during the puerperium

Injections of 3 mg of estradiol benzoate were given to seven lactating women during the second and third weeks postpartum to study its effects on secretion of follicle-stimulating hormone (FSH) and prolactin during the subsequent 4 days. Administration of estradiol during te second week postpartum had no effect on serum levels of FSH and prolactin, however, 1 week later estradiol injection elicited a double effect: FSH levels decreased and prolactin concentrations increased. Early lactation seems to abolish the estrogen induced positive feedback effect on pituitary gonadotropin secretion. The negative effect of estrogen on FSH secretion and the positive effect on prolactin release became evident by the third week postpartum.