In all irradiated monkeys, tubular cross-sections were observed that did not contain any germ cells (Fig. 1A). Only 4 of the 29 irradiated monkeys had no repopulation at all (RI = 0%). This was found in one of the two monkeys that received a dose of 8 Gy, in one of the three that received 8.5 Gy, and in both that received two fractions of 6 Gy each with an interval of 24 h. For monkeys in which repopulation did take place, the seminiferous epithelium was usually normal and complete in those tubular crosssections in which germ cells were present, with all generations of spermatogenic cells being present. Comparing the diameter of the normal (see below) tubular cross-sections with full spermatogenesis in irradiated and in control monkeys, no difference was found (169 ± 4 ^m [n = 29] vs. 169 ± 3 ^m [n = 10], respectively).
In 25 of the 29 irradiated monkeys, seminiferous tubules with a dilated lumen were seen in one or both testes (Fig. 1, A and B). Dilation of tubules with and without spermatogenesis was observed. In 25 of the 58 irradiated testes, the extent of the tubular widening was such that it was not possible to measure the tubular diameter of normal tubules. Tubular widening might occur because of obstructed flow of the tubular fluid secreted by Sertoli cells. Therefore, serial sections were made to see whether occlusions were in the lumen of the widened tubules. No such occlusions were found. Also, dilated tubules were seen ending on the rete testis (Fig. 1B), suggesting an obstruction in the rete testis or the epididymis. However, serial sections of these organs also did not reveal any evidence of obstruction.
FIG. 1. A) Testicular section of an irradiated monkey. In all irradiated monkeys, tubular cross-sections without any germ cells were seen (asterisks). When tubular cross-sections contained germ cells, the seminiferous epithelium was mostly normal (dots). In many monkeys, the tubular lumen of some seminiferous tubules was dilated (arrowheads). X90. B) Dilated tubules were sometimes seen to connect to the rete testis (arrow). The arrowhead indicates a seminiferous tubule with a normal lumen connecting to the rete testis. X90. C) Seminiferous tubular cross-section showing normal spermatogenesis as well as an area with densely packed, abnormal Sertoli cells (arrow). Nuclei of normal Sertoli cells are indicated by arrowheads. X500. D) Higher magnification of the area in C with abnormal Sertoli cells (arrow). X1250. E) Tubular cross-section lacking germ cells but showing an area with abnormal Sertoli cells (arrow). Note the difference in the density of the nuclei in the abnormal area compared to that in the rest of the tubule. X500. F) Epididymis of an irradiated monkey. Spermatozoa are indicated by asterisks. X125. Bar = 30 ^m.