Relation between sex hormone binding globulin and D-norgestrel levels in plasma

In order to investigate the effect of changes in sex hormone binding globulin (SHBG) levels on d-norgestrel (d-Ng) levels in plasma, the plasma levels of SHBG and d-Ng were studied during one treatment cycle in 6 women on oral contraceptives containing d-Ng and ethinyloestradiol (EOE2) and in 3 women using subcutaneous silastic rods containing d-Ng concomitantly taking EOe2 for three weeks. A significant positive correlation between the SHBG and d-Ng levels was found in 7 of the 9 subjects studied. The results provide evidence for an in vivo binding of d-Ng to SHBG, a SHBG influence on the metabolic clearance rate of d-Ng and consequently a dependence of the plasma levels of d-Ng on the SHBG concentrations in the plasma. These findings support the concept that the clinically and biochemically observed anti-oestrogenic/androgenic effects observed in women on d-Ng containing medication are due to a displacement of testosterone from SHBG by d-Ng.