The Effect of Temperature upon Ultraviolet Carcinogenesis with Wave Lengths 2,800-3,400 A*

Since the discovery of the carcinogenicity of ultraviolet radiation, work on this subject has been directed toward specification of the wave lengths involved and determination of the energy requirements of the process (1, 2, 3, 8). A filter for the isolation of wave lengths 2,800-3,400 * was described and the production of tumors with this portion of the spectrum reported in a previous publication from this laboratory (1). However, the efficiency of carcinogenesis was not so great as when the whole spectrum of the mercury arc was used, and there seemed to be some other factor or factors that affected carcinogenesis. The present report deals with the investigation of one of these factors, namely, temperature. One difference in the irradiation of mice with filtered as compared to unfiltered radiation was that i n the latter treatment more heat energy was received by the animals. Heat is known to increase the effect of roentgen irradiation on the skin of young rats (4, 5) and presumably the response to ultraviolet irradiation might likewise depend upon the temperature. Moreover, it has been shown that high environmental temperatures (92 ~ F.) increase the rate of development of subcutaneous methylcholanthrene tumors and of transplantable methylcholanthrene tumors (10). perature. One group was placed in a thermostatically controlled oven at 35-38 ~ C. during irradiation. It was necessary to equip the oven with forced ventilation to control the humidity and to insure survival of the mice. Another group was placed in an insulated, ice-cooled box at approximately 3-5 ~ C. while being irradiated. A control group was irradiated at room temperature in the usual manner (1). In the first two cases the mice were subjected to the irradiation temperatures for a 30 minute equilibration period before the irradiation was begun. Evans, Goodrich, and Slaughter (5) have reported that the rectal temperature rapidly approaches that of the skin at low and high temperatures. It is likely, however, that with our method of cooling the body temperature of the mice did not fall more than a few degrees. In all cases the mice were irradiated 30 minutes a day, 6 days a week, with the light of a medium pressure mercury vapor lamp 1 passed through a filter previously described (1), which isolated the wave lengths 2,800-3,400 A. The energy incident upon the irradiation cage was measured with a multiple junction copper-constantan thermopile in conjunction with a high sensitivity galvanometer (1). All groups received an intensity of approximately 4,200 ergs/ cm.2/sec, resulting in a daily dose of about 0.75 • 107 ergs/cm.2