Abstract
OBJECTIVE: It has been suggested that the high prevalence of subnormal free testosterone concentrations, along with low or inappropriately normal gonadotropins in men with type 2 diabetes, may be the result of an increase in plasma estradiol concentrations secondary to an increase in aromatase activity in the adipose tissue that leads to the suppression of the hypothalamo-hypophyseal-gonadal axis. RESEARCH DESIGN AND METHODS: To investigate this hypothesis, plasma estradiol, testosterone, leutinizing hormone, follicle-stimulating hormone, and sex hormone-binding globulin (SHBG) concentrations were measured in fasting blood samples of 240 men with type 2 diabetes. Free estradiol concentrations were either calculated (n = 198) using total estradiol and SHBG measured by immunoassay or directly measured by liquid chromatography tandem mass spectrometry (LC-MS/MS) and equilibrium dialysis (n = 102). RESULTS: The calculated free estradiol concentration in men with subnormal free testosterone concentrations was lower than that in men with normal free testosterone concentrations (median 0.047 vs. 0.063 ng/dL, P < 0.001). Directly measured (LC-MS/MS) free estradiol concentrations were also lower in men with subnormal free testosterone concentrations (median 0.025 vs. 0.045 ng/dL, P = 0.008). Free estradiol concentrations were directly related to free testosterone but not to BMI or age. CONCLUSIONS: These data show that the suppression of the hypothalamo-hypophyseal-gonadal axis in patients with subnormal free testosterone concentrations and type 2 diabetes is not associated with increased estradiol concentrations. The pathogenesis of subnormal free testosterone concentrations in type 2 diabetes needs to be investigated further.