THE RECOVERY FROM VARIOUS GRADATIONS OF CELL LOSS IN THE MOUSE SEMINIFEROUS EPITHELIUM AND ITS IMPLICATIONS FOR THE SPERMATOGONIAL STEM CELL RENEWAL THEORY

The recovery of the seminiferous epithelium from cell loss has been investigated by counting the different kinds of A-spermatogonia and resting primary spermatocytes in stages 7–8 of the cycle of the seminiferous epithelium at different intervals of time after injection of several dose levels of the alkylating agent Myleran. It was found that the decrease in total number of A-spermatogonia is directly related to the logarithm of the dose of Myleran given. After all doses used, the total number of A-spermatogonia starts to increase again between day 8 and 10. During the first part of the recovery, between day 8 and 16, the number of morphologically undifferentiated A-spermatogonia increases, its maximal value being linearly dependent on the logarithm of the dose of Myleran given. Between day 24 and 32, the total number of A-spermatogonia overshoots control values significantly only when large doses of Myleran are used, no overshoot having been observed at low doses. This suggests the existence of an all or none relationship between overshoot and cell loss. The number of resting primary spermatocytes never overshoots control values. The results are discussed as to the information they might give on the numerical behaviour of the stem cells of spermatogenesis.