Sex hormone binding globulin: the carrier protein for d-norgestrel

Abstract

The binding of different synthetic steroids, used in hormonal contraception, to Sex Hormone Binding Globulin (SHBG) was studied by measuring their ability to displace tritiated testosterone from SHBG in a competitive protein binding system. Only 19-nortestosterone derivates had any significant ability to displace testosterone from SHBG, d-norgestrel (d-Ng) being the strongest displacer. Increasing the SHBG levels in women with previous constant plasma d-Ng levels increased these levels two- to sixfold. It is concluded that SHBG is the main carrier protein for d-Ng. The strong testosterone displacing activity of d-Ng might also explain androgenic side effects observed with d-Ng containig oral contraceptives.