A quantitative assessment of the gametogenic and androgenic properties of testicular steroids in hypophysectomized rats.

The ability of testicular steroids to maintain the quantitative aspects of spermatogenesis was compared with reference to their androgenic properties. Hypophysectomized rats were injected daily with 0.2 mg progesterone, 20 alpha-dihydroprogesterone, 3 beta-hydroxy-5 alpha-pregnan-20-one, testosterone or testosterone propionate for 30 days beginning 2 days after the operation. Testosterone propionate was the most potent steroid tested both in terms of its peripheral androgenic effects and its ability to prevent the post-operative decline in the weight of the testis and seminiferous tubules and the numbers of germ cells throughout their differentiation. The natural androgen, testosterone, exhibited weak gametogenic properties and only partly maintained the normal measures of spermatogenesis. Progesterone exhibited low intrinsic androgenic potency yet was significantly more effective than testosterone in maintaining spermatogenesis; it prevented the degeneration of spermatocytes during the later stages of meiotic prophase and the reduction divisions resulting in an increased yield of step 7 spermatids. Low androgenic and gametogenic properties were exhibited by 20 alpha-dihydroprogesterone and 3 beta-hydroxy-5 alpha-pregnan-20-one. These results may indicate that testosterone produced locally in the seminiferous tubules from progesterone is more effective in maintaining spermatogenesis than androgens entering from the circulation. Alternatively, progesterone may act more directly on the germ cells than previously envisaged.