The female guinea pig, a useful model for the genetic hazard of radiation in man; preliminary results on germ cell radiosensitivity in foetal, neonatal and adult animals.

A comparison was made of the radiosensitivities of the resting oocyte of guinea pig in its two different states, the 'large' resting and 'contracted' oocyte, also extending the investigations to the radiosensitivity of the female germ cells at earlier stages during intrauterine life. The radiosensitivity of guinea pig oocytes was evaluated by testing the fertility of the animals 6 months and 1 year after irradiation of the ovaries with high doses (2 or 4 Gy) of X-rays. Animals had been treated in utero (target cells: oogonia and oocytes at leptotene), at birth (target cells; resting oocytes of the large type) or as adults (target cells: resting oocytes of the contracted type). No loss of fertility was evident, even 1 year after treatment, whatever the stage or dose. These investigations were completed by histological studies of the ovaries from treated and control animals. Irradiation induced a dose-dependent decrease in the total number of oocytes, and this effect was more pronounced in animals irradiated as adults (target cells: contracted resting oocytes). Our results also suggested that the LD50 of the large guinea pig resting oocyte should be around 4 Gy, a value similar to that obtained recently for the equivalent human oocyte. This confirms the high radioresistance of the guinea pig oocyte and the consequence suitability of this species for further detailed studies in relation to genetic hazards in man.