Effects of Sodium Pentobarbital on the Radiation Response of EMT6 Cells in Vitro and EMT6 Tumors in Vivo

Sodium pentobarbital is frequently used to anesthetize experimental animals and veterinary patients to immobilize them for radiotherapy. The effects of this agent on the radiation response of the EMT6 cells in culture and EMT6 tumors in mice were examined. Sodium pentobarbital in concentrations of 0.050 and 0.25 mg/ml was not toxic to oxic or hypoxic cells and did not alter the radiation dose-response curves of aerated or hypoxic cell cultures. Recovery from potentially lethal damage and sublethal damage was not altered in cells exposed to sodium pentobarbital throughout the recovery period. In vivo, anesthetization with sodium pentobarbital did not alter the survival curve for cells suspended from tumors which had been rendered hypoxic before irradiation, but did alter the survival curve for cells from tumors in air-breathing mice, probably because of an increase in the hypoxic fraction in these tumors. Anesthesia with sodium pentobarbital immediately after irradiation did not alter recovery from sublethal or potentially lethal damage. Sodium pentobarbital had no direct effect on the radiation response of cells in culture or in tumors. However, the physiologic effects of the drug on the host produced environmental alterations, including changes in the temperature and oxygenation of the tumor, and altered themore » response of the tumor cells to irradiation.« less