Effect of testicular extracts on proliferation of spermatogonia in the mouse.

Two intraperitoneal injections with an interval of 4 h between them, of rat testicular extract into adult male mice causes a decrease in the production of A spermatogonia in the compartment of undifferentiated A (As, Apr and Aal) spermatogonia. A significant decrease in the total number of A spermatogonia in stages VII and VIII of the cycle of the seminiferous epithelium was found at 2, 4 and especially 5, 7 and 8 days after treatment. Extracts of rat liver and rat spleen were without effect. In addition, an extract of rat testis containing very few spermatogonia had no effect. It was concluded that the active substance in the extract is synthesized and/or specifically accumulated in the spermatogonial compartment of the testis. Thus the active substance is tissue-specific but not species-specific, since extracts of both rat and bull testes were effective after injection into mice. It is inferred from the data that the effect of injection of testicular extracts is unlikely to be due to cytotoxicity, hormonal changes in the tubular environment or to an immunologic reaction, but is probably due to a spermatogonial chalone. This chalone partially inhibits proliferation of early type A spermatogonia in the normal mouse testis.