[Periodic compensation reactions in the course of postnatal growth of mouse liver following fractionated roentgen radiation during embryogenesis. 1].

Following daily fractionated X-irradiation in utero, a postnatal study of the mouse liver was made with regard to compensatory growth responses depending on the radiation dose and on the age of the germ while irradiated. Exposure to doses between 10 R/d and 60 R/d was performed during blastogenesis (1st to 5th day p.c.), organogenesis (6th to 13th day p.c.), fetogenesis (14th to 18th day p.c.), as well as during the early (6th to 10th day p.c.) and the late embryogenesis (11th to 15th day p.c.). Besides deviations of the increase in weight and of the nucleic acid content, the incorporation of 3H-thymidine into DNA was measured by means of scintilation counts and radioautographs. As compared with controls, all irradiated experimental groups exhibit a periodical increase of the proliferative hepatic growth especially towards the end of the first and of the second post-natal week. The possibility of inducing compensatory responses decreases, however, with increasing age of the germs, a gradation thus appearing from overcompensation effects after exposures during blastogenesis down to poor proliferation responses after irradiations in the course of fetogenesis. The dose dependence of proliferation responses after irradiations during organogenesis is characterized by an overstrain of the capacity for recovery following 60 R/d, by maximum compensatory growth after 40 R/d, and by a slight stimulation of growth following 10 R/d, in the otherwise apparently normal animals. Late proliferative responses of the developing liver are regarded as a self-stabilisation towards the predetermined norm of growth. Essential differences in comparison with a stress - or a strain - stimulated growth (as in the adult regenerating liver) are suggested by the observation that (a) cytogenesis in the functionally independent populations of blood cells and of parenchymal cells is stimulated partly at the same time and to a similar extent, (b), that stimulation effects reach a peak always within equal stages of development independent of the X-ray doses and the age at irradiation and (c) that an acceleration of growth is possible with a normal or even augmented ratio of organ-weight to body-weight.