Temperature and Radiosensitivity of Skin of New-Born Rats

Abstract

For many years occasional reports have appeared in clinical and experimental literature suggesting the possibility of increasing or decreasing the amount of injury produced by a given dosage of roentgen radiation by controlling the metabolic rate of the cells. These reports have usually suffered from one or more of the following difficulties: lack of adequate control of the metabolic rate of the biologic material; lack of careful and quantitative analysis of the results; difficulty of applying conclusions derived from the study of the lower animals to mammalian tissue. An attempt has been made to answer the above objections by using mammalian tissue (skin of new-born rats), the metabolic rate of which responds rapidly to changes in environmental temperature and which is relatively sensitive to roentgen radiation. It was found in the first investigation (1) that the radioresistance of the skin of new-born rats was greatly increased by chilling the animals to or near 0° C. during the irradiation. A method of measuring the radiation injury was devised (2), and it was found that for the cold-treated animals the threshold dosage was raised and that above this point the injury increased less rapidly with increased dosage than it did in animals irradiated at room temperature. In the third investigation (3) new-born rats were irradiated at temperatures ranging from 0 to 40° C., and it was found that the radiosensitivity increased in proportion to the rise in temperature. The purpose of the present investigation was to determine whether the temperature could have acted through its control of such metabolic processes as rate of blood circulation and breathing. This was done by lowering the metabolic rate by means other than low temperature. The exposure time in all experiments was fifteen minutes and the dosage was 2,010 roentgens. The target distance was 30 em. The radiation was unfiltered, except for 2-mm. cardboard, and the half value layer was about 1.5 mm. aluminum. Effect of Reduced Breathing Rate During Irradiation on Relative Radiosensitivity It was found that a new-born rat could be taped so tightly that it could not breathe, and could be revived after fifteen to twenty minutes of this treatment. A condition approaching anoxia was produced and this greatly increased the radioresistance of the skin, as can be seen in Fig. 1. The resistance, as indicated by failure of the radiation to produce epilation, was about the same as that of the rat irradiated at 6° C. and was greater than that of the one treated at 17° (breathing rate reduced but not completely stopped). Histologic examination of the skin irradiated while the breathing was blocked indicated that the injury corresponded to that of only 900 roentgens to animals irradiated at 28° C. while breathing freely. The experiment was repeated, and again the animal whose breathing was blocked during irradiation proved to be very radioresistant.