SEX HORMONE-BINDING GLOBULIN AND FEMALE REPRODUCTIVE FUNCTION

Although sex steroids have long been known to influence serum concentr ations of SHBG, it is now recognized that nutritional factors may be m ore important in the regulation of SHBG in women. Thus, SHBG concentra tions are negatively correlated with body mass index (BMI) and, more p articularly, to indices of central adiposity. Polycystic ovary syndrom e (PCOS), the most common cause of anovulatory infertility, is associa ted with truncal obesity, hyperandrogenism and hyperinsulinaemia. Ther e is evidence that insulin may be the humoral mediator of the weight-d ependent changes in SHBG. Serum SHBG concentrations are inversely corr elated with both fasting and glucose-stimulated insulin levels, and in sulin has been shown to have a direct inhibitory effect on SHBG synthe sis and secretion by hepatocytes in culture. However, the interrelatio nship of BMI, insulin and SHBG appears to be different in women with P COS from that in normal subjects. The clinical importance of the weigh t-related suppression of SHBG is illustrated by the finding of a great er prevalence of hirsutism in obese women with PCOS compared with thei r lean counterparts. Obese subjects with PCOS have similar total testo sterone concentrations to lean PCO women but have lower SHBG and recip rocally higher free testosterone levels. Calorie restriction results i n reduction of serum insulin followed by an increase in SHBG and a fal l in free testosterone but an isocaloric, low-fat diet has no signific ant effect on SHBG concentrations. Weight reduction in obese, hyperand rogenaemic women with PCO is an important approach to the management o f both anovulation and hirsutism.