Thirteen pre-pubertal and fifteen sexually mature rhesus monkeys (Macaca mulatta) were subjected to 1000 to 12,000 r unilateral X-irradiation; the contralateral ovary served as a control. The ovaries were removed at intervals of 6 hr to 4 weeks later, and the numbers of normal and atretic oocytes at each stage of follicular maturation were counted in every 40th section of both treated and control gonads.
Doses of 4000 to 12,000 r induced cytoplasmic eosinophilia in oocytes, pyknosis in many granulosa cells and the destruction of most of the multi-layered follicles. The changes became more marked as the post-irradiation interval was extended.
The numbers of primordial oocytes were unaffected by exposure to less than 3000 r; such oocytes were, however, almost totally eliminated 7 days after treatment with 12,000 r. The LD50/30 for germ cells at this developmental stage is about 5000 r. Oocytes enveloped by more than one layer of granulosa cells were more radio-sensitive, only a small proportion surviving for 4 days after exposure to 4000 r. Ovaries recovered 25 days following irradiation with 5000 to 12,000 r contained few multi-layered follicles ; most of the germ cells were atretic and the granulosa cells pyknotic.
The primordial oocyte of the rhesus monkey is markedly resistant to radiation-induced cell death (following the terminology of Mandl, 1964), and contrasts sharply with the primordial oocytes of other mammalian species.