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The Response of the 9 1/2-Day-Old-Rat Embryo to Variations in Exposure Rate of 150 R X-Irradiation

BRENT, ROBERT L. The Response of the 91-Day-Old-Rat Embryo to variations in Exposure Rate of 150 R X-Irradiation. Radiat. Res. 45, 127-136 (1971). A review of the literature dealing with irriadiated rodent embryos indicates that continuous irridation with exposure rates below .005 R/min or 5 R/day is not measurably deleterious to the surviving offspring. In the experiments described herein, 9-day-old rat embryos were irradiated with 150 R at four exposure rates (100, 34, 1.5, and 0.5 R/min). The results indicate that protraction of this dose of irradiation reduces the lethal, malforming, and growth retarding effects of the irradiation. Since protraction of the radiation to the embryo reduced the severity of growth retardation and the incidence of malformation, it is reasonable to conjecture that these effects are interrelated. Thus, it would seem most appropriate to study the dynamics of irreparable growth retardation with the tools of the cell biologist before attacking the more complicated problem of the mechanism of teratogenesis. When the problem of teratogenesis is approached, the studies reported here would indicate that it would be well to concentrate on one or several malformations. These protraction studies have yielded at least five malformations that do not occur following a low exposure-rate but are present in a high exposure-rate group, both groups having received 150 R. It is by studying these special instances with the newer techniques available and by concentrating on the mechanism of irreversible growth retardation that a better understanding