Radiolethal and genetic vulnerabilities of germ cells in the female mammal: Effects of tritium and other radiations compared

Our focus is on the nature of the lethality target in very sensitive cells. In the mouse, several types of radiations have now been used, including 3H-Tdr incorporated into oocyte DNA, gamma rays delivered at various dose rates, 250 kVp x rays, neutrons of various energies, and three kinds of accelerated heavy ions (Si14+, Ar18+, Fe26+). We have shown that the lethality target in mouse immature oocytes is non-nuclear; it is equal in cross-sectional area to the entire oocyte and is separated from the nucleus by about 4 μm. A substantial body of data now points to the plasma membrane as the lethality target in these particular cells. We have quantified both chromosome aberrations and dominant lethal mutations in oocytes from females exposed 8 to 12 weeks earlier. Results from these and other studies show that: (1) for immature oocyte killing in mice, chronically administered 3HOH is of near maximum biological effectiveness, similar to the most effective neutrons and heavy ions (likely true also for female germ-cell killing in some prenatal primates), (2) tritium incorporated into DNA as 3H-Tdr is about 100 times less effective in mouse immature oocyte killing than is tritium administered as 3HOH, and (3) for mutagenicity in the mouse, immature oocytes appear to have approximately the same sensitivity as mature oocytes and show dose and LET responses similar to those obtained from genetic studies of other cells. The possible implications of these findings for women exposed to tritium are considered