Murine in vivo L-band ESR spin-label oximetry with a loop-gap resonator

Small mice (approximately 20 g) were anesthetized and placed in a loop-gap resonator of diameter 25 mm resonating at 1.1 GHz. An oxygen-permeable capsule containing 2.5 X 10(-2) M perdeutero 15N TEMPONE (1-oxyl-2,2,6,6-tetramethyl-4-piperidone) in light paraffin oil was implanted in the peritoneal cavity. Electron spin resonance (ESR) spectra from the capsule are sensitive to the concentration of dissolved oxygen and calibration curves are given. The oxygen concentration was found to rise from a value close to zero when the animal breathes air to a level of 220 microM when the animal breaths pure oxygen. It is speculated that this surprisingly high level is related to the effect of the anesthetic on the cardiovascular system. Encapsulation provides a barrier to spin-label reductants and to paramagnetic metal ions that might confound the spin-label oximetric measurements.