Androstenedione is a steroid hormone and the major precursor to testosterone. It is available without prescription and taken with the expectation that it will be converted to testosterone endogenously and increase strength and athletic performance. The metabolism of orally administered testosterone has not been well studied.
We randomly assigned 37 healthy men to receive 0, 100, or 300 mg oral androstenedione in a single daily dose for 7 d. Single 8-h urine collections were performed on the day before the start of the androstenedione administration and on d 1 and 7 to assess excretion rates of free and glucuronide- conjugated testosterone, androsterone, etiocholanolone, and dihydrotestosterone. Serum testosterone glucuronide concentrations were measured by frequent blood sampling over 8 h on d 1 in 16 subjects (5 each in the 0 and 100 mg group and 6 in the 300 mg group).
In the control group, mean (±se) d 1 and 7 excretion rates for testosterone, androsterone, etiocholanolone, and dihydrotestosterone were 3 ± 1, 215 ± 26, 175 ± 26, and 0.4 ± 0.1 μg/h, respectively. In the 100 mg group, mean d 1 and 7 excretion rates for testosterone, androsterone, etiocholanolone, and dihydrotestosterone were 47 ± 11, 3,836 ± 458, 4,306 ± 458, and 1.6 ± 0.2 μg/h, respectively. In the 300 mg group, mean d 1 and 7 excretion rates for testosterone, androsterone, etiocholanolone, and dihydrotestosterone were 115 ± 39, 8,142 ± 1,362, 10,070 ± 1,999, and 7.7 ± 1.5μ g/h, respectively. Urinary excretion rates of all metabolites were greater in both the 100 and 300 mg groups than in controls (P < 0.0001). Urinary excretion rates of testosterone (P = 0.007), androsterone (P = 0.009), etiocholanolone (P= 0.0005), and dihydrotestosterone (P < 0.0001) were greater in the subjects who received 300 mg androstenedione than in those who received 100 mg. In the treated groups, excretion of free testosterone accounted for less than 0.1% of the total excreted testosterone measured. Serum testosterone glucuronide levels increased significantly during frequent blood sampling in both the 100 and 300 mg groups compared with controls (P = 0.0005 for the 100 mg group; P < 0.0001 for the 300 mg group). The net mean changes in area under the curve for serum testosterone glucuronide were −18 ± 25%, 579 ± 572%, and 1267 ± 1675% in the groups receiving 0, 100, and 300 mg/d androstenedione, respectively.
We conclude that the administration of both 100 and 300 mg androstenedione increases the excretion rates of conjugated testosterone, androsterone, etiocholanolone, and dihydrotestosterone and the serum levels of testosterone glucuronide in men. The magnitude of these increases is much greater than the changes observed in serum total testosterone concentrations. These findings demonstrate that orally administered androstenedione is largely metabolized to testosterone glucuronide and other androgen metabolites before release into the general circulation.