Influence of age on the response of rat stem spermatogonia to -radiation.

Abstract

Testes of Sprague–Dawley rats aged either 2 or 12 months were administered 285 rads of 60Co γ-radiation at 45 rads/min. Irradiated animals along with controls (10 per group) were killed at postirradiation intervals varying from 5 to 120 days. Irradiation effects were assayed through testicular weights and counts of type-A spermatogonia in 50 cross sections of seminiferous tubules at stages 5 to 8 of the spermatogenic cycle. No significant difference in number of type-A spermatogonia was observed in testes of nonirradiated rats between the ages of 2 and 16 months. Irradiation reduced spermatogonial numbers to 21 to 25% of control in both age groups, but the postirradiation interval at which it occurred was different—day 5, 2 months; day 10, 12 months. By 24 days after irradiation, spermatogonial numbers had increased to 55% of control in 2-month testes, but 12-month testes were only at 40% of control. The magnitude of the difference between young and old did not change at later postirradiation stages. At 80 days after irradiation, spermatogonial numbers peaked at 90% of control in 2-month testes and 74% of control in 12-month testes. Percents of control at 120 days postirradiation were 84 and 70% for 2- and 12-month testes, respectively. These results lead to the conclusion that irradiation produces a permanent decrement in the stem spermatogonial population with the magnitude of the decrement being age dependent.