Studies on the adaptive response in mouse female germ cells X-irradiated in vitro at two different stages of maturation

Radioadaptation is a phenomenon whereby cells exposed to a low dose (conditioning dose) of ionizing radiation are more resistant to a dose in the order of a few Gy (challenge dose) delivered some time thereafter. It is generally postulated that radioadaptation could result from the activation of damage repair and/or antioxidant defence systems. We used a recently developed in vitro system to investigate the possibility of a cytogenetic adaptive response in female germ cells X-irradiated at 2 well characterized stages of maturation. Mouse ovarian follicles were cultured from an early preantral stage (1-2 layers of follicle cells) up to ovulation. Hormonal stimulation of ovulation was realized by addition of hCG and EGF to the culture medium on day 12. The follicles were X-irradiated with either 2 or 4 Gy preceded or not by 50 mGy (“conditioning dose”, 5 h earlier), on days 0 or 12 of the culture. Ovulated oocytes were collected on day 13, fixed and analyzed for the presence of chromosome aberrations. The results suggested that pre-irradiation of mouse pre-ovulatory oocytes with a low conditioning dose of X-rays could confer them some protection against radiation-induction of chromosome damage by a subsequent challenge dose of a few Gy.