Intriguingly, effects of irradiation on the morphology of Sertoli cells were found in eight monkeys. Possibly, irradiation at the time these cells were not yet terminally differentiated and still proliferating, and/or the abnormal hormone levels induced by the disappearance of most of the germ cells, altered some of the Sertoli cells. The appearance of these aberrant cells was hyperplastic-like, but no evidence for tumor formation was seen.
In rodent studies, no effects of irradiation on tubular width and Sertoli cell morphology have been reported. Unlike in the LBNF1 rat, no arrest of spermatogenesis was seen in the monkey, because the repopulated tubules generally showed full spermatogenesis. However, the present study was carried out at a very long time after irradiation, and a transient disturbance in spermatogenesis at an earlier interval after irradiation may have taken place.
The nonaffected concentrations of testosterone indicate that Leydig cell function in the monkeys was not influenced by these doses of irradiation, as was reported earlier for adult rats that had been irradiated pre- or neonatally or when they were adults. Because the larger part of circulating estradiol is formed peripherally from testosterone in the male monkey, that estradiol levels also did not change is not surprising. The lack of effect of the dose range studied is consistent with data in the human, indicating that, in boys, only doses of 20 Gy or more affect Leydig cell function.
The correlation between levels of inhibin and FSH in male mammals has been studied before. Reports in which the presently used sandwich assay with antibodies against both the inhibin a and (3 subunits was used showed a negative correlation between levels of inhibin B and FSH in normal and infertile men. In the latter two publications, levels of inhibin B were directly related to quantitative aspects of spermatogenesis, as observed in testicular biopsies. The significant inverse relationship between inhibin and FSH levels in the monkeys indicates that the inhibin B immunoassay can be used to assess the concentration of biologically active inhibin in this species. Furthermore, inhibin levels provide a good indication of the quantity of spermatogenesis, as in the human.