Effects of d-norgestrel induced decreases in sex hormone binding globulin capacity on the d-norgestrel levels in plasma

Abstract

The effect on the plasma sex hormone binding globulin capacity (SHBGc) and the relation between the plasma SHBGc and the plasma concentration of the synthetic (d-Ng) steroid has been studied in women treated with ovulation inhibiting doses of d-norgestrel and medroxyprogesterone acetate (MPA). The steroids were administered by means of steroid impregnated Silastic intravaginal rings (IVRs). In the women using d-Ng impregnated IVRs the SHBGc was depressed to subnormal levels. After treatment the SHBGc returned to normal within three weeks. A close correlation between the SHBGc and the d-Ng concentration was found when the dose of d-Ng delivered from the IVR was about 200 μg per day or more. Oral administration of 250, 500 and 1000 μg of d-Ng resulted in doubling of the plasma concentration d-Ng on doubling of the d-Ng dose. These results suggest that at a certain SHBG level, the plasma concentraition of d-Ng is dose dependent and that at a certain d-Ng dose level, the plasma concentration of d-Ng is SHBG dependent. No effect on the SHBGc and no correlation between the SHBGc and the MPA concentration was found in the women using IVRs impregnated with MPA. The results show that the decrease in SHBGc found in women on d-Ng is not due to anovulation or decreased estradiol levels in plasma.