Responses of the Rat to Thermal Radiation

¹ From the Department of Physiology, University of Pennsylvania Medical School, Philadelphia, Naval Aviation Medical Acceleration Laboratory, Johnsville, Pennsylvania, and Hoffmann-LaRoche, Inc., Nutley, New Jersey

Using the method of rapid measurement of skin temperature during exposure to known amounts of thermal radiation, the ‘thermal inertia’ or kpc product (k = thermal conductivity, p = density, c = specific heat) was measured for the rat skin. An average kpc value of 84 ± 18 x 10^–5 cal²/cm⁴/sec/°C² was obtained for the lightly anesthetized animal. This value was independent of the intensity of the radiation, the method of exposing the skin; i.e., shaving, clipping, or depilating, and anesthesia. Administration of 200 mg/kg of azapetine phosphate, a potent adrenolytic agent, was accompanied by a marked drop in skin temperature (4–5°C), but no statistically significant change was observed in the kpc values when compared with the controls. Unanesthetized animals were exposed to high intensity thermal radiation and the animals' reactions observed. Two reactions could be identified, the skin twitch and the escape or withdrawal reactions, occurring at average skin temperatures of 45–46°C and 51–52°C, respectively. A possible correspondence of these reactions to those previously observed to occur in man at these temperatures; i.e., pain threshold and wince threshold, was noted.