THE METABOLISM OF STEROID HORMONES IN SEMEN

SUMMARY Testosterone is converted reversibly to androstenedione by the spermatozoa of certain mammals, such as the boar and stallion. The oxidation of testosterone to androstenedione occurs not only in the presence of fully active spermatozoa but also of sperm cells which have been deprived of their normal motility, and fructolytic as well as respiratory activity, by such treatment as cold-shock or deep-freezing. However, heating or treatment with certain inhibitors (e.g. cyanide and cetyltrimethylammonium bromide) renders the spermatozoa incapable of performing the testosterone ⇌ androstenedione reaction. The enzyme system required for that reaction has been obtained in the form of a cell-free extract from disintegrated boar spermatozoa. There is some evidence that it involves both NAD+ and NADP+. Oestradiol-17β is converted reversibly to oestrone. The reaction oestradiol → oestrone has been demonstrated in bull, boar and stallion semen, and the reverse reaction in boar and stallion semen. Progesterone is also metabolized in semen. The product may be 20β-hydroxy-pregn-4-en-3-one.