In five of the six control monkeys, spermatogenesis was normal, even in the two monkeys that were older than 30 yr. In the sixth monkey, which was 18 yr of age, spermatogenesis was poor for no apparent reason. This last monkey was not taken into account in all comparisons between normal and irradiated monkeys.
In the seminiferous epithelium of 8 of the 29 irradiated monkeys, patches or whole tubular cross-sections with aberrant Sertoli cells were found. These abnormal Sertoli cells were densely packed, with no germ cells in between these cells (Fig. 1, C-E). One of the most striking examples is shown in Figure 1, C and D, in which it can be seen that such a thick layer of Sertoli cells is still compatible with normal spermatogenesis. Aberrant Sertoli cells were not observed in the control monkeys.
In the dose-response group, the extent of repopulation of the seminiferous epithelium by surviving spermatogonial stem cells was studied by determining the percentage of tubular cross-sections showing germ cells (i.e., the RI) in each monkey (Fig. 2A). These results appeared to be rather variable. The correlation between the RI and the dose was only just significant (P = 0.036), and in view of this, no D0 value (i.e., the dose killing 63% of the stem cells) as a measure of x-ray-induced spermatogonial stem cell death was calculated. A more reliable dose-effect relationship was found when the irradiation dose was compared to testicular weight (P = 0.003) (Fig. 2B).
FIG. 2. A) Dose-response relationship for spermatogonial stem cell killing as determined by counting the percentage of repopulated seminiferous tubular cross-sections (RI) in testes of adult rhesus monkeys that received graded doses of x-rays prepubertally (n = 19 testes [10 animals, one testis not available], P = 0.036). B) Effect of graded doses of x-rays, given prepubertally, on adult testicular weight in rhesus monkeys (n = 19 testes [10 animals, one testis not available], P = 0.003).