Regulation of the density of spermatogonia in the seminiferous epithelium of the Chinese hamster: II. Differentiating spermatogonia.

In this study the yield of the proliferation of the differentiating spermatogonia into spermatocytes was determined in five Chinese hamsters. Large differences of up to a factor 2 were found between the numbers of A1 spermatogonia in the various animals. However, the numbers of leptotene spermatocytes varied only by up to a factor 1.2 between animals. It is concluded that more spermatogonial degeneration takes place in animals with a relatively large number of A1 spermatogonia than in those with a small number of these cells. In such a way in all animals ultimately about the same number of spermatocytes is formed. An experiment was done in which the number of A1 spermatogonia was lowered with the S-phase killer cytosine arabinoside (Ara-C). It was found that this greatly increased the yield of the spermatogonial proliferation, showing a direct relationship between the number of A1 spermatogonia in an animal and the extent of the spermatogonial degeneration. In addition to the variation in the number of A1 spermatogonia found between various animals, an even larger variation of up to a factor 3.7 was found between the numbers of A1 spermatogonia in different areas of seminiferous tubules within each animal. Nevertheless the variation in the number of leptotene spermatocytes in different areas within each animal was not larger than a factor 1.3. It is concluded that in the normal animal the phenomenon of spermatogonial degeneration depends on the local density of these spermatogonia. Apparently, when too many spermatogonia are present the surplus of cells degenerates.