Hypothalamic gliosis by MRI and visceral fat mass negatively correlate with plasma testosterone concentrations in healthy men

OBJECTIVE: To determine whether a relationship was evident between gliosis in the mediobasal hypothalamus (MBH) and plasma testosterone concentrations in men METHODS: 41 adult men (ages 18–50 years) from 23 twin pairs underwent fasting morning blood draw and brain MRI. T2 relaxation time was used to quantify gliosis in the MBH and control areas in the putamen and amygdala. Plasma concentrations of testosterone and 17β-estradiol were measured by LC-MS/MS. Body composition including visceral adiposity was measured by dual X-ray absorptiometry. RESULTS: A negative association was found between MBH T2 relaxation time and plasma concentrations of both free and total testosterone (r = −0.29, P<0.05 and r = −0.37, P<0.01, respectively). Visceral adiposity exhibited a negative correlation with plasma total testosterone concentration (r = −0.45, P=0.001) but a positive correlation with MBH T2 relaxation time (r = 0.24, P=0.03). The negative correlation between plasma total testosterone and MBH T2 relaxation time remained significant after adjustment for visceral adiposity, age, BMI, and insulin resistance. CONCLUSIONS: In healthy men across a range of BMIs, MBH gliosis was associated with higher visceral adiposity but lower endogenous testosterone. These findings suggest that MBH gliosis could provide novel mechanistic insights into gonadal dysfunction in men with obesity.