| Summary: | The administration to normal men of supraphysiological doses of testosterone causes a profound inhibition of spermatogenesis and is currently being investigated as a method of male contraception. Azoospermia, however, is achieved in only 50-70% of men, the remainder maintaining a very low rate of spermatogenesis. The object of these studies was to investigate the biochemical basis for the maintenance of spermatogenesis in the oligozoospermic group, and in particular to investigate the hypothesis that the activity of the enzyme 5α-reductase, which converts testosterone to the more potent androgen dihydrotestosterone (DHT), is increased in these men either constitutionally or as a result of treatment. Thirty-three normal men were recruited to a clinical trial of hormonal male contraception. After a baseline period, subjects were administered 200 mg testosterone oenanthate i.m. weekly. Semen samples were analysed at 4 weekly intervals. When the sperm density had fallen below 5 million/ml in 3 consecutive samples, the subjects were required to discontinue all other forms of contraception for one year, during which the weekly injections of testosterone were continued. 18 of the subjects became azoospermic within 20 weeks of testosterone treatment, the other 15 remained severely oligozoospermic with a mean sperm density of 2.0 ± 0.8 million/ml at that time. Multiple blood sampling over the week following the first injection and after 16 weeks of testosterone treatment demonstrated that there were no differences in plasma concentrations of total or bioavailable testosterone or of oestradiol between the two groups of men. Similarly, the rate and degree of suppression of gonadotrophin secretion was similar in the two groups.
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