31P NMR spectroscopic and near infrared spectrophotometric studies of effects of anesthetics on In vivo RIF‐1 tumors. relationship to tumor radiosensitivity

Abstract

Mice with subcutaneous RIF-1 tumors were anesthetized with sodium pentobarbital (PB) or ketamine plus acepromazine (KA) before acquisition of in vivo ³¹P nuclear magnetic resonance (NMR) spectra from tumors. The area of the inorganic phosphate resonance was significantly greater (relative to phosphomonoesters or the α-phosphate resonance of nucleoside triphosphate) in spectra obtained under PB anesthesia, suggesting that the hypoxic fraction of the tumor increased following PB anesthesia. In vivo near-infrared laser spectroscopy directly demonstrated that tumor oxyhemoglobin was reduced by more than 20% following PB but was not significantly affected by KA. Total hemoglobin (tumor blood volume) was reduced by 11% following PB anesthesia, but was not significantly affected by KA. Tumor growth delay induced by γ-irradiation was shorter when tumors were irradiated under PB anesthesia than when irradiated under KA, showing that PB anesthesia had a radioprotective effect. These studies demonstrate that both the ³¹P NMR and near infrared methods can detect metabolic or physiological changes associated with an increase in tumor radioresistance (i.e., an increase in the radiobiological hypoxic fraction).