Effect of Dose-rate (γ-radiation) on the Mitotically-active and Differentiating Germ Cell of the Prenatal Male Rat

Summary

Rat foetuses, aged 15, 17, or 19 days of gestation were subjected to 95 rads of ⁶⁰Co γ-radiation administered at rates of 0·95, 9·5 or 45 rads/min and examined 6, 28, and 49 days after birth. Dose-rate effects were assayed at day 6 by enumerating germ cells in 150 cross sections of seminiferous tubules and measuring testicular weights. At days 28 and 49, dose-rate effects were determined by means of testicular weights and counts of fertile and sterile tubular cross-sections.

Germ-cell survival was inversely related to age at irradiation. Dose-rate effects were pronounced (P < 0·05) in testes iradiated at day 15 (germ cells mitotically active), equivocal at day 17 (germ cells mitotically active and differentiating), and absent at day 19 (germ cells differentiating only). Both testicular weights and tubular counts measured at day 28 were apparently directly related to the germ-cell counts.

The mitotically-active gonocyte was comparatively refractory to the necrotizing effects of ionizing radiation, and the degree of refractoriness was materially influenced by dose-rate. Conversely, the gonocyte undergoing differentiation was highly susceptible to the cell-killing effects of irradiation and the degree of susceptibility was little influenced by the dose-rate.