Increased number of IGF-I receptors on erythrocytes of women with polycystic ovarian syndrome

OBJECTIVE: TO test the hypothesis that insulin acts though ovarian IGF- I receptors to produce excessive amounts of androgens in polycystic ovarian syndrome (PCOS), by measuring the binding capacity of IGF-I receptors on erythrocytes and relating the findings to the degree of hyperandrogenism and hyperinsulinaemia. DESIGN: A case-control study of IGF-I receptors on erythrocytes of women with PCOS and age- and weight-matched controls. PATIENTS AND METHODS: IGF-I receptors on erythrocytes, serum levels of androgens, IGF-I, GH, basal insulin and insulin response during oral glucose tolerance test (oGTT) were measured after induced or spontaneous withdrawal bleeding in 10 women with PCOS and eight normo-ovulatory women. RESULTS: An increased number of IGF-I receptors was found on erythrocytes of patients with PCOS compared with the controls (P < 0.01), irrespective of their body mass index. Serum IGF-I levels were similar in both groups. The degree of hyperinsulinaemia, provoked by oGTT, correlated positively with basal insulin (r = 0.69; P = 0.003), but not with the number of IGF-I receptors. However, the number of IGF-I receptors correlated positively with androstenedione (r = 0.54, P = 0.0018). CONCLUSIONS: The findings in the present study that the number of IGF-I receptors and not the insulin levels correlate with serum androstenedione support the theory that the hyperandrogenism in PCOS is not a direct effect of the hyperinsulinaemia, but IGF-I mediated.