EFFECT OF A SPERMATOGONIAL CHALONE ON THE GROWING RAT TESTIS

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Abstract
Immature rats were used in an experiment to test the possible influence of a spermatogonial chalone on the expanding spermatogonial population in their developing testes. An extract from adult rat testes was injected i.p. into 33-day-old rats and control animals were injected with an equal amount of saline. Two groups of normal adult rats similarly injected with the testicular extract and saline solutions served as additional controls. Following these injections, all animals were administered a dose of 3H-thymidine 10 h before sacrifice. An analysis of the labeling indices of the various types of spermatogonia revealed that in young rats injected with testicular extract the percentage of labeled type A spermatogonia was significantly lower than in control animals. In contrast, the labeling indices of intermediate and type B spermatogonia were similar in the 2 groups of young rats. In the 2 groups of adult animals, there was no difference in the labeling indices of type A or of other types of spermatogonia. The saline extract of adult testes contained a spermatogonial chalone substance inhibiting specifically the proliferation of some type A spermatogonia. Apparently, a spermatogonial chalone may intervene through its action on the spermatogonial stem cell population to arrest the growth of the seminiferous tubules as the animal reaches maturity.