Direct relationship between elevated free testosterone and insulin resistance in hyperprolactinemic women

Women with hyperprolactinemia have been reported to have hyperandrogenemia and/or insulin resistance. However, little is known about the association of hyperandrogenemia and insulin resistance in these women. To investigate whether hyperandrogenemia and/or insulin resistance occur in hyperprolactinemic women, and to assess the relationship between them, we measured basal androgen level and both glucose and insulin levels after oral glucose administration in 20 hyperprolactinemic women and 7 female control subjects. Free testosterone level was higher and estradiol level lower in hyperprolactinemic women than in control subjects (p < 0.05), whereas dehydroepiandrosterone sulfate (DHEAS) and total testosterone levels were similar (p > 0.05). Both fasting glucose and insulin levels didn't differ in the two groups (p > 0.05). However, both serum glucose and insulin levels, after a 75 g glucose load, were significantly increased in hyperprolactinemic women, (p = 0.001, p < 0.001, respectively). In simple linear regression analysis in hyperprolactinemic women, only free testosterone level had a positive correlation with the incremental area under the insulin curve (insulin-IAU) (r = 0.47, p < 0.05). In multiple stepwise regression analysis, free testosterone level, mean blood pressure and DHEAS level were associated significantly with insulin-IAU (beta = 0.98, p < 0.0001; beta = 0.58, p = 0.002; beta = -0.67, p < 0.003, respectively). These results suggest that insulin resistance is closely related to elevated free testosterone level in hyperprolactinemic women.