Metabolic clearance rate of testosterone in male epileptic patients on anti-convulsant therapy

Abstract

There are several reports which state that male epileptics on anti-convulsant therapy have reduced sexual activity. We and others have shown that, although total testosterone is raised, the free testosterone concentration is reduced in this patient population. This could be a result of an increased metabolic clearance rate (MCR) of testosterone, inadequate secretion of LH to stimulate testosterone synthesis or inappropriately low testosterone production by the Leydig cells. We have examined these possibilities by measuring the MCR of testosterone in 15 male epileptics on anti-convulsant therapy. In this group of patients, the mean LH (9.3 +/- 5.9 IU/l) and sex-hormone binding globulin (SHBG) (54.5 +/- 22.9 nmol/l) concentrations were significantly greater than those of five normal control subjects (4.7 +/- 1.11 IU/l and 26.0 +/- 7.0 nmol/l respectively). Mean total testosterone concentrations of the two groups were not significantly different but the mean percentage of free testosterone and free testosterone concentration were significantly lower in the patient population (2.06 +/- 0.43 vs 2.98 +/- 0.27 and 0.56 +/- 1.1 vs 0.79 +/- 0.07 pmol/l). The MCR of testosterone was significantly lower in the patients (773 +/- 322 vs 1354 +/- 443 l/day) and showed a positive correlation with the percentage of free testosterone. Therefore, our results suggest that the lowered free testosterone in male epileptics on anti-convulsant therapy is not due to an increased MCR of testosterone. The increased LH concentration suggests primary hypogonadism. This, in turn, could be responsible for low free testosterone levels in the presence of normal testosterone.