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The Effects of Fluoxymesterone Administration on Testicular Function

The University of Chicago Pritzker School of Medicine and the Biomedical Center for Population Research Chicago, Illinois

Long term daily administration of fluoxymesterone (9-fluoro-17-methyl-llβ, 17β- dihydroxyandrost-4-en-3-one) was associated with a modest suppression of sperm production and a profound suppression of testosterone levels in the absence of significant effects on plasma gonadotropin levels. Nine normal male volunteers took either 10, 20, or 30 mg of fluoxymesterone daily for twelve weeks. Plasma samples were obtained for testosterone, estrogen, LH and FSH levels at biweekly intervals before, during and for up to 12 weeks after fluoxymesterone treatment. Samples were obtained for dehydroepiandrosterone sulfate, testosterone binding globulin and free testosterone assays at representative times before, during and after treatment.

Although lower sperm counts were observed at several points during both the treatment and follow up periods, significant consistent suppression spermatogenesis could not be demonstrated. Reduced plasma testosterone levels were seen within 24 h after beginning fluoxymesterone, and further reductions were noted throughout the treatment period. Changes in plasma estrogen levels did not correlate with fluoxymesterone administration. Neither plasma LH nor plasma FSH levels were significantly altered by fluoxymesterone.

A short term study utilizing a single dose of fluoxymesterone yielded similar findings.

It is proposed that fluoxymesterone has a local effect on the Leydig cell which is not mediated by gonadotropins.

Supported by the following grants: USPHS HD-70152, USPHS HD-06308, HD-07110 and RR 55.

Presented in part at the 56th Annual Meeting of the Endocrine Society.

¹ Gerald Sokolec Foundation Fellow in Endocrinology.

Received July 7, 1975.