Abstract: OBJECTIVE: To investigate the effects of ⁶⁰Co γ rays on testosterone secretion and testicular histopathology of male Beagle dogs. METHODS: 15 male Beagle dogs were subdivided into 3 groups:the control group and the irradiation groups. Irradiation groups were exposed to 0.5 Gy or 5.0 Gy ⁶⁰Co γ ray,dosage rate 0.5 Gy/min. At the 4^th-,7^th-,14^th-,28^th- and 60^th-day after irradiation,the content of serum testosterone was determined by the competitive inhibition immunoassay. And at 60^th day after irradiation,the testicles were obtained for observation and histopathology. RESULTS: During 10-13 days after irradiation,all the animals of the 5.0 Gy γ ray irradiation group died,and hemorrhage spots were found on their testes and epididymises. At 60th day after irradiation,there was no difference statistically between the 0.5 Gy γ ray irradiation group and the control group. The testicle average weight of 0.5 Gy group was 69% of the control group,while there was no statistical difference for testicle/body weight ratio between the 0.5 Gy γ ray irradiation group and the control group. Meanwhile,at 4^th-,7^th-,14^th-,28^th-and 60^th-day after irradiation,there was no statistical difference for serum testosterone content among the 0.5 Gy γ ray irradiation group and blank control group. Spermatogenic cells from the 0.5 Gy and 5.0 Gy γ ray irradiation groups showed necrosis and lysis. In addition,azoospermia generation wasn't found in the testicle of the 5.0 Gy group. CONCLUSION: Acute 0.5 Gy and 5.0 Gy γ ray irradiation induced damage to the reproductive system of male Beagle dogs:the testicle structure, spermatogenic cells and azoospermia generation were severely damaged. However,serum testosterone content did not show much obvious changes,

Key words: ⁶⁰Co γ ray, Beagle dog, irradiation damage, testosterone, testes, histopathology