CIRCULATING OXYTOCIN AND VASOPRESSIN IS INFLUENCED BY OVARIAN-STEROIDREPLACEMENT IN WOMEN

Background. The posterior pituitary hormones appear to be involved in the etiology of primary dysmenorrhoea, but mechanisms regulating their release, particularly the influence of ovarian steroids, are not full y understood. Methods. The effect of 17 beta-estradiol and medroxyprog esterone alone and in combination on oxytocin and vasopressin levels w as therefore studied in 10 postmenopausal women. Results. Transdermal treatment with estradiol alone by means of patches in a dose of 100 mu g/24 h for five days resulted in an elevation of the mean plasma conc entration of this hormone from undetectable to 262 pmol/l and increase in mean circulating levels of vasopressin from 0.82 to 1.22 pmol/l an d of oxytocin from 2.50 to 3.98 pmol/l. Oral administration of medroxy progesterone in a dose of 10 mg per day for 5 days, which resulted in a mean plasma level of 4.3 nmol/l, suppressed vasopressin concentratio ns to 0.60 pmol/l. When given after five days of treatment with estrad iol, medroxyprogesterone also antagonized the stimulatory effect of th e estrogen on vasopressin secretion. Medroxyprogesterone alone increas ed the plasma oxytocin concentration to 3.26 pmol/l, but the progestog en did not significantly influence the stimulatory effect of estradiol on oxytocin secretion. Conclusions. It is concluded that posterior pi tuitary hormone secretion is influenced by estradiol and progestogens, and that this may be a mechanism for the involvement of ovarian hormo nes in the etiology of primary dysmenorrhoea.