Effects of 10 Days Administration of Percutaneous Dihydrotestosterone on the Pituitary-Testicular Axis in Normal Men

Abstract

Dihydrotestosterone (DHT) was administeredpercutaneously in a dose of 125 mg twice daily for 10 days to 12 normal men. Basal plasma levels of testosterone (T), 17β3-estradiol (E²), and LH were measured every 2 days in these men and every 5 days in subjects from a control group receiving placebo. The daytime course of plasma hormone levels between two DHT applications was studied in six men. LRH tests were performed in nine men before and on day 10 of DHT administration. Plasma levels of free T and free E²) and T-E-binding globulin capacity and affinity were measured in six men before and on days 5 and 10 of DHT administration. Before DHT administration, there was no difference in basal plasma levels of T, DHT,E², and LH between the control and the DHT-treated group. In the latter group, plasma DHT levels increased sharply from 0.52 ± 0.05 (±SE) to 3.70 ± 0.92 ngβml on day 2 (P < 0.001) during DHT treatment. Plasma T, E², and LH levels decreased significantly from 7.33 ± 0.74 to 1.33 ± 0.54 ngβml (P < 0.001), from 46 ± 5 to 20 ± 3 pgβml (P < 0.01), and from 7.8 ± 1 to 4.2 mlUβml (P < 0.05),respectively. Except for a small decrease in plasma DHT (P < 0.05) 12 h after the previous DHT application, hormone levels were stable during the time between the two DHT treatments. The responses of LH and FSH to LRH were not different before and on day 10 of DHT administration. Plasma levels of free T and free E² as well as those of total T and E² decreased; however, the percentages of unbound T and E² were not different before and during DHT administration. T-E-binding globulin capacity and affinity were not modified by DHT administration. Changes in plasma DHT levels were negatively correlated with those in plasma T and LH. The results of this study demonstrate that 10-days DHT administration has an inhibitory effect on the hypothalamo-pituitary-testicular axis in normal men.