Comparative aspects of the effects of radiation during oogenesis

Abstract

Primordial germ cells, which are relatively resistant to radiation administered prior or during migration, become sensitive during sex differentiation of the gonad. Sensitivity increases to a maximum during the peak “wave” of mitosis in oogonia, and especially during the final premeiotic division. The oocyte subsequently becomes increasingly resistant to radiation as it progresses from leptotene to pachytene, after which sensitivity increases with the onset of the period of arrested development (diplotene or dictyate stage). Oocytes vary considerably in radiosensitivity with: ( i) age, ( ii) species, ( iii) inbred or outbred strain, ( iv) stage of growth of the follicle which surrounds the oocyte, and ( v) chromosomal configuration. Those in primordial follicles are highly sensitive in mice, rats and rabbits; moderately sensitive in dogs, cows and pigs; and highly resistant in the guinea pig, monkey and human. The response of oocytes in multi-layered follicles is less variable (2000–4000 R). Reproductive capacity in the irradiated mammal closely parallels the size of the surviving population of oocytes, but the latter appear to be used more efficiently than in controls. The marked species differences in the response of oocytes cannot be fully explained at present. The most important factors are now known to be chromosomal configuration and metabolic activity. A hypothesis to explain differential radio-sensitivity is described.