Cyclosporine inhibits testosterone biosynthesis in the rat testis.

To determine whether the immunosuppressive agent cyclosporine (CsA) has an effect on testicular androgen function in the male rat, four groups of adult animals were treated daily for 28 days with either orange juice or three doses of CsA (7.5, 15, or 30 mg/kg X day). Twenty-four hours after the last dose of CsA, the animals were killed and the following parameters were measured: testis, seminal vesicle, and ventral prostate weights; serum levels of CsA, creatinine, testosterone (T), and LH; and intratesticular levels of pregnenolone, progesterone, 17 alpha-hydroxyprogesterone, androstenedione, and T. There were no differences between the control (orange juice) and the three CsA-treated groups with respect to serum creatinines and testis, seminal vesicle, and ventral prostate weights. Serum T decreased significantly in the 15 and 30 mg/kg CsA-treated groups. The intratesticular T level decreased significantly only in the 15 and 30 mg/kg CsA-treated groups. In the 15 and 30 mg/kg CsA-treated groups, the intratesticular pregnenolone, progesterone, and 17 alpha-hydroxyprogesterone levels all showed a significant decline compared to controls. There was no significant change in the androstenedione levels in any of the CsA-treated groups. To determine whether the decrease in T production by the testis exposed to CsA is via inhibition of the hypothalamic-pituitary axis, serum LH was measured in all four groups. Serum LH decreased significantly only in the 15 and 30 mg/kg CsA-treated groups. These data suggest that oral CsA administration in doses greater than 15 mg/kg X day results in diminished intratesticular T production that appears to be mediated via inhibition of pituitary LH function.