Osmotically-induced release of vasopressin and oxytocin in non-pregnant women--influence of estrogen and progesterone.

Background: Circulating vasopressin and oxytocin are influenced by ovarian steroid blood levels, but the effect of estrogen and progestogen treatment on induced release of the posterior pituitary hormones is not clear.

Methods: Eight postmenopausal women who had not been on hormonal replacement therapy for at least two months were included in the study. The women were treated for four weeks with transdermal administration of estradiol-17beta in a daily dose of 100 microg with the addition of 5 mg tablets of medoxyprogesterone twice daily for the last two weeks. A 25 minute intravenous infusion of hypertonic saline (0.06 mg/kg/min) was given before hormonal treatment, and after two and four weeks with serial plasma sampling for assay of vasopressin and oxytocin.

Results: The mean basal concentration of vasopressin, which was 0.83+/-0.13 (SE) pmol/L before hormonal treatment, increased to a statistically significant degree after estradiol alone to 1.18+/-0.11 pmol/L and decreased after combined estrogen/progestogen treatment to 0.31+/-0.02 pmol/L. Sodium concentration and osmolality increased in a similar way during all three infusions, but the resultant increase in vasopressin concentration was significantly smaller and slower after treatment with estradiol alone than in the first experiment without pretreatment. The areas under the concentration curve for the second and third infusion were significantly smaller than when no hormone treatment was given. The induced hyperosmolality also caused a rise in oxytocin levels, but no influence of ovarian hormone treatment was observed.

Conclusions: Ovarian hormone administration influences vasopressin secretion, affecting both the basal levels in plasma and the responses to an increase in plasma osmolality. The influence of ovarian hormones on oxytocin secretion is minimal.