SPERMATOGENESIS IS ACCELERATED IN THE IMMATURE DJUNGARIAN AND CHINESE-HAMSTER AND RAT

The rate of progression of spermatogenesis was studied in immature Dju ngarian and Chinese hamsters and Wistar rats by scoring the most advan ced cell types present at various ages after birth. From 15 days of ag e onward, the most advanced cell types in the Djungarian hamsters were formed at a rate compatible with the duration of the spermatogenic cy cle in adult animals, i.e., 7.9 days. However, in Djungarian hamsters up to 15 days of age, the rate of spermatogenic development was accele rated. The estimated duration of the spermatogenic cycle ranged betwee n 5.0 and 5.3 days. In the rats, spermatogenesis also was accelerated during the first 15 days of life, with an estimated duration of the se miniferous cycle of 4.5-5.3 days. From 15 days of age onward, the rate of progression was strongly reduced, being compatible with the adult value of 12.8 days. In the Chinese hamsters, a similar change in the r ate of spermatogenesis occurred at 25 days. Before this age, spermatog enesis proceeded with an estimated duration of the cycle of 8.8-9.2 da ys. From 25 days onward, spermatogenesis advanced much more slowly, at a rate compatible with the adult value of 17.0 days. Despite the stro ng reduction in the rate of spermatogenic progression in the three spe cies, the cellular associations in the stages of spermatogenesis were not affected. In the three species, the clear reduction in the rate of spermatogenic progression correlated with the process of testicular d escent, with the appearance of pachytene spermatocytes associated with preleptotene spermatocytes, and with the onset of tubular lumen forma tion. Possible causes for the reduction in the rate of spermatogenesis may be a shift to a lower temperature due to testicular descent, or a change in the level of a Sertoli cell-secreted factor(s) concomitant with the differentiation of these cells.