EFFECT OF ANESTHETICS ON THE RADIOSENSITIVITY OF A MURINE TUMOR

The effect of four anesthetics on implanted MT tumors was investigated. Compared with unanesthetized animals, no change in radiosensitivity was observed if mice were irradiated under either tribromoethanol or fentanyl-fluanisone-diazepam anesthesia. However, a small but significant degree of radioprotection was observed under chloral hydrate or pentobarbital anesthesia. Hypothermia or increased hypoxia are considered unlikely mechanisms for the protection, a direct chemical action being most probable. The preferred method for immobilizing the mice in order to irradiate the tumors locally was by simple physical restraint (with care taken to minimize physiological stress). However, if anesthesia was a necessity, the present work suggests that for the MT tumor at least the 'non-protecting' tribromoethanol and fentanyl-fluanisone-diazepam are preferable to the fentanyl-fluanisone-diazepam in that it produces a smaller drop in temperature. However, it is only a short-acting anesthetic, and prolongation of the state of anesthesia by repeated doses simply prolongs the temperature decline so that there may be no real benefit over fentanyl-fluanisone-diazepam.