[Effects of several estrogenic compounds on serum corticosteroid-binding globulin (CBG) and the estrogen thresholds...

The effects of several estrogen substances--alone, or in combination with norgestrel--on serum CBG in humans are reported in this paper. CBG was measured by a modified charcoal adsorption technique. Daily oral doses of Premarin, from 0.3 to 2.5mg, were given to healthy postmenopausal women for 14 days. Dose-dependent increases in CBG-BC were observed. Ovral, which contains ethinylestradiol and norgestrel, also induced significant increases in the levels of CBG-BC. Similar results were seen with Lo Ovral, but it had less influence than Ovral. When given alone, daily for 21 days, norgestrel had no effect on CBG-BC. The maximum rise of serum CBG-BC was found after 10 days of the daily doses of Ovral, and then the levels remained quite constant during the period of treatment. Exogenous estrogens of other types also caused increases in CBG-BC. The response of CBG to exogenous estrogens is of use in comparing the estrogen potencies of the compounds. CBG-BC levels remained constant throughout the menstrual cycle in five normal women despite fluctuating levels of estradiol which reached peaks of 190 approximately 430 pg/ml. In pregnant women and in HMG-treated women, however, serum levels of CBG-BC increased beginning when estradiol levels were greater than 1 ng/ml.