PHENYTOIN-INDUCED ELEVATION OF SERUM ESTRADIOL AND REPRODUCTIVE DYSFUNCTION IN MEN WITH EPILEPSY

Reproductive and sexual dysfunction in men with epilepsy has been attributed to androgen deficiency. Low serum free testosterone (FT) levels occur in both hypogonadotropic and hypergonadotropic hypogonadism. Antiepileptic drugs (AEDs) have been implicated. Proposed mechanisms include induction of increased sex hormone binding globulin (SHBG) resulting in decreased FT, as well as dysfunction or premature aging of the hypothalamopituitary-gonadal axis. In an investigation comparing serum reproductive steroid levels among 20 men receiving phenytoin (PHT) monotherapy for complex partial seizures, 21 untreated men with complex partial seizures, and 20 age-matched normal controls, total estradiol levels were significantly higher in the PHT group (56.3 +/- 29.4 pg/ml, mean +/- SD) than in the untreated (32.4 +/- 27.4 pg/ml, p < 0.01) and normal control (34.3 +/- 12.7 pg/ml, p < 0.05) groups. The physiologically active non-SHBG-bound serum estradiol levels were also significantly higher in the medicated group (45.1 +/- 21.7 pg/ml) than in the untreated (29.9 +/- 17.2 pg/ml, p < 0.01) and normal control (31.1 +/- 11.4 pg/ml, p = 0.05) groups. These findings suggest that PHT may lower FT by induction of aromatase, enhancing FT conversion to estradiol, as well as SHBG synthetase. Estradiol exerts a potent inhibitory influence on luteinizing hormone secretion and has been suggested to play a major role in negative feedback in men as well as women. Suppression of LH secretion results in hypogonadotropic hypogonadism. Chronically low FT leads to testicular failure and hypergonadotropic hypogonadism. Finally, estradiol has been shown to produce premature aging of the hypothalamic arcuate nucleus, which secretes gonadotropin-releasing hormone.