An "in vitro" system for the study of rat spermatogonial proliferative control.

The effect of a "testicular extract" on spermatogonial proliferation in adult rats is comparatively studied both "in vivo" and "in vitro". Both in irradiated rats injected with "testicular extract" as in testicular fragments from irradiated rats incubated in culture medium, addition of "testicular extract" elicits an inhibition in thymidine-H3 uptake by type A spermatogonia. This is not the case for non irradiated rats or incubation of testicular samples from non irradiated animals after addition of "testicular extract". The "in vitro" system for assay of the spermatogonial chalone is used to analyze the general characteristics of this mitotic inhibitor.