The induction by ionizing radiation of chromosomal aberrations in rhesus monkey pre-meiotic germ cells: effects of dose rate and radiation quality.

The induction of reciprocal translocations in rhesus monkey stem-cell spermatogonia was studied using multivalent analysis at metaphase of primary spermatocytes. Animals were exposed to 1 Gy gamma-rays at dose rates of 140 and 0.2 mGy/min or to 0.25 Gy acute 2 MeV neutrons. Reduction of the dose rate from 140 mGy/min to 0.2 mGy/min did not result in a lowering of the frequencies of recovered translocations of 0.43%. The neutron data indicated an RBE (neutrons vs. X-rays) of 2.1, which is clearly lower than the value of 4 obtained in the mouse. It is made plausible that in general mammalian species with high sensitivities for the cytotoxic effects of ionizing radiation, such as the rhesus monkey, will exhibit relatively high threshold dose rates below which no further reduction in aberration yield occurs, whereas in more resistant species, such as the mouse, the threshold dose rate will be at a very low level. Similarly, resistant species will show relatively high RBE values for neutron irradiation and sensitive species low ones.