Laboratory monitoring of androgenic activity in benign prostate hypertrophy treated with a 5 alpha-reductase inhibitor.

Testosterone and androstenedione are metabolized by 5 alpha- and 5 beta-reductases to androsterone (A) and etiocholanolone (E), respectively. These are excreted in the urine as conjugates, and the A/E ratio in normal men is usually greater than or equal to 1.5 (as opposed to 1 in women) because of the high 5 alpha-reductase activity in the prostate. The A/E ratio can be determined simply by gas chromatography after acid hydrolysis of a urine sample, extraction of steroids, and formation of trimethylsilyl derivatives. A timed collection of urine is unnecessary because the ratio of A/E is used rather than absolute values. In men suffering from benign prostate hypertrophy who are treated with Finasteride (a 5 alpha-reductase inhibitor), the A/E ratio decreases to less than 0.5. The A/E ratio decrease can be detected long before there is clinical improvement.