Inhibin B in Men with Severe Obesity and After Weight Reduction Following Gastroplasty

Abstract

Although the effect of obesity on some gonadal functions in men is known, its effect on Sertoli cell function has not been reported. We tested the hypothesis that the serum inhibin B level is decreased in men with severe obesity, and that this change persists after significant weight loss. We measured gonadal hormones in 17 obese men before (baseline) and after weight reduction following silastic ring vertical gastroplasty (SRVG). Their baseline body mass index (BMI) was 44.3 ± 1.7 kg/m2, mean ± standard error of the mean (SEM). Seven of 16 obese men (44%), compared to 8 of 69 reference men (12%), had a baseline inhibin B level below 100 pg/ml (p < 0.01). A weak inverse association was found between inhibin B and BMI before weight reduction (r = −0.494, p = 0.072). Furthermore, FSH levels, which were weakly inversely associated with inhibin B levels (r = −0.482, p = 0.059), were inappropriately unelevated in 5 of the 7 obese men with low (below 100 pg/ml) inhibin B. After a weight reduction of 40 ± 2.6 kg, mean ± SEM, following surgery, the obese men’s BMI was 31.6 ± 1.5 kg/m2, mean ± SEM, and inhibin B normalized in 3 of the 7 patients with low inhibin B. Despite weight reduction, FSH remained inappropriately unelevated in 2 of the 4 patients whose inhibin B remained low. This study also confirmed previously published findings that obese men have low serum total and free testosterone and relative hypogonadotropic (low LH) hypogonadism that may persist after weight reduction. In conclusion, Serum inhibin B levels in obese men may be low. This may be due to relative hypogonadotropic (also low FSH) hypogonadism.