Decrease and Recovery of Ejaculated Sperm Concentration after Acute Testicular Gamma-Ray Irradiation in Cynomolgus Monkeys (Macaca fascicularis)

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After acute testicular irradiation in adult male cynomolgus monkey semen was periodically collected, and sperm concentration was examined as an index of radiation damage to the seminiferous epithelium. Sperm concentrations decreased after irradiation with 1, 2, or 3 Gy. Concentrations fell below the minimum normal level for unirradiated monkeys, (10⁷ sperm /ml of semen [13]) at 16.0, 8.5, and 8.0 weeks after irradiation, respectively. The lowest sperm concentra-tion was observed 17.0, 12.5, and 14.0 weeks after irradiation, and the percentages of the lowest sperm concentration relative to the pre-irradiation concentration were 1.20, 1.37, and 0.20%, respectively. The sperm concentration recovered to pre-irradiation levels after 35.5, 36.5 and 41.0 weeks at doses of 1, 2 and 3 Gy, respectively. These results indicate that spermatogenesis decreases markedly after irradiation with 1-3 Gy but resumes after a definite period that depends on the radiation dose. Sperm concentration can be utilized as an effective index of radiation damage to the seminiferous epithelium and as an index of recovery.