Causes of Male infertility - Gonadotoxins

A. Radiation
The effects of radiotherapy on sperm production are well described. They are derived mainly from a series of remarkable experiments performed during the "atomic age" but only recently published. In a study of healthy prisoners in Oregon and Washington in the 1960s, Clifton and Bremner (1983) examined the effects of ionizing irradiation on semen quality and spermatogenesis. Before a vasectomy, each of 111 volunteers was exposed to different levels of radiation, from 7.5 to 600 cGy. Sperm counts were analyzed weekly and each prisoner served as his own control. There was a distinct dose-dependent, inverse relationship between irradiation and sperm count. A significant reduction in sperm count was observed at 15 cGy, and sperm counts were temporarily abolished at 50 cGy. Azoospermia was induced at 400 cGy in 4 of 5 patients; this persisted for at least 40 weeks. Despite these profound effects, sperm counts rebounded to preirradiation levels in most patients during recovery.

From examination of testis tissue after irradiation, it was concluded that spermatogonia are the germ cells most sensitive to irradiation. Given the dramatic sensitivity of testis tissue to irradiation, subsequent studies have focused on the "scatter" to testes of men undergoing radiation therapy for cancer. In patients subjected to abdominal radiation with gonadal shielding, the estimated mean unintended gonadal exposure was approximately 75 cGy. There does not appear to be an increase in congenital birth defects in offspring of irradiated men.

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