SPERMATOGONIAL CELL-PROLIFERATION IN ORGAN-CULTURE OF IMMATURE RAT TESTIS

Regulatory mechanisms of male germ cell proliferation in mammals were investigated by using in vitro organ culture of immature rat testis. N utritional and hormonal requirements for maintenance and differentiati on of germ cells in vitro were first characterized by testing differen t culture conditions. FSH was essential for the progression of type A spermatogonia up to the stage of pachytene spermatocytes after 3 wk of in vitro culture, while vitamins A, C, and E, 1,H, and testosterone w ere not effective. The proliferative activity of Sertoli cells markedl y declined after 1 wk of in vitro culture, irrespectively of the prese nce of FSH in the medium. In addition, basal testosterone production b y Leydig cells was maintained after 1 wk of culture, provided that FSH was present in the medium. The appearance of differentiating type I a nd type B spermatogonia and meiotic cells in the seminiferous cords th roughout culture was accompanied by a significant reduction in the num ber of undifferentiated spermatogonia. Moreover, a similar labeling in dex of undifferentiated spermatogonia was observed in both unstimulate d and FSH-stimulated testis fragments at all culture times considered. Therefore, FSH did not influence the mitotic activity of undifferenti ated spermatogonia, suggesting a differential role of this gonadotropi n during the mitotic phase of spermatogenesis. These results indicate that the organ culture system of immature rat testis represents a usef ul experimental model for studying regulatory mechanisms of spermatogo nial cell proliferation.