In the present investigation, the peak of apoptosis, occurring during the first spermatogenic wave in rat testis, was found to be related to the stage of spermatogenesis even at a very early age. As in the case of the adult testis, in 18- and 26-day-old rat testis a high frequency of apoptosis was observed in cells at spermatogenic stages IX-I, whereas the corresponding frequency associated with stages II-VI was low. In contrast, the frequency of apopto-sis connected with stages VII and VIII of mature spermatogenesis was low, but this same frequency was much higher in the immature rat testis. These observations suggest that the early increased apoptosis essential for later development occurs during immature stages VII-VIII.
In the immature rat testis, two groups of cells have been shown here to be especially prone to apoptosis. Type A spermatogonia were observed to die by apoptosis at 8 days of age, and furthermore, these cells accounted for a major proportion of the apoptotic cells in immature spermatogenic stages IX-I in older animals. This death of type A spermatogonia was associated with their maximal rate of mitosis in the same stages of the cycle; in addition, apoptotic A spermatogonia were surrounded by a large number of other, nonapoptotic A spermatogonia. These results support the earlier hypothesis that in the mammalian testis, the rate of degeneration of type A spermatogonia is density-dependent. buy zyrtec online