Although the original experiments were not done to study long-term effects on the testis, the irradiated monkeys were divided in three groups. A control group was also included and consisted of six monkeys ranging from 7 to 35 yr of age (mean age, 21 yr).
First, a group of 10 monkeys received doses ranging from 4 to 8.5 Gy of 6 MV x-rays (one monkey, 4 Gy; two monkeys, 5 Gy; three monkeys, 6 Gy; one monkey, 7 Gy; two monkeys, 8 Gy; and one monkey, 8.5 Gy), which was called the dose-response group. The ages of the animals at the time of irradiation were 28 (n = 1), 29 (n = 3), 30 (n = 1), 31 (n = 1), 35 (n = 1), 39 (n = 1), 42 (n = 1), and 46 (n = 1) mo (mean age, 34 mo). The animals were killed at intervals of 77-92 mo (mean interval, 84 mo) after irradiation. The age at death in this group varied between approximately 9 and 11 yr. This group was used to study the dose-response relationship for killing of spermatogonial stem cells in the prepubertal monkey.
Second, an interval group of 13 monkeys received 5 Gy of 300 kV x-rays. The ages of the animals at the time of irradiation were 17 (n = 1), 25 (n = 1), 30 (n = 1), 36 (n = 1), 38 (n = 3), 39 (n = 4), 41 (n = 1), and 47 (n = 1) mo (mean age, 36 mo). The animals were killed at intervals of 38-79 mo after irradiation. The age at death in this group varied between approximately 6 and 10 yr. This group was used to study the capacity of the seminiferous epithelium to recover from the irradiation by outgrowth of repopulating colonies founded by surviving spermatogonial stem cells.
Third, a group of six monkeys received various irradiation treatments. Two monkeys (at 30 and 33 mo of age) received 4 Gy and one monkey (at 33 mo) 8.5 Gy of 300 kV x-rays as described above. One monkey (at 53 mo) received 8.5 Gy of 6 MV x-rays. Furthermore, two monkeys (at 17 and 50 mo) received two doses of 6 Gy of 6 MV x-rays given 24 h apart. The age at death in this group varied between approximately 7 and 12 yr.
To study translocation induction by irradiation, a selection was made of all irradiated monkeys (see below).