MEASUREMENT OF PO2 IN LIVER USING EPR OXIMETRY

With the use of India ink and lithium phthalocyanine (LiPc) as electro n paramagnetic resonance (EPR) oximetry probes, the PO2 of the liver w as investigated in mice. Because India ink was taken up by the Kupffer cells of the liver, the EPR signal of the India ink reflected the ave rage PO2 in phagocytic vesicles of these cells. The mean value of PO2 in the Kupffer cells measured by India ink was 15.3 +/- 4.4 Torr in un anesthetized animals. LiPc was administered as a macroscopic crystal a nd therefore reflected the PO2 of the overall liver. The PO2 measured by LiPc was 23.4 +/- 4.4 Torr, which is consistent with the median val ue of 23.5 Torr reported previously with the use of an oxygen electrod e. Anesthesia (injection of 60 mg/kg ip pentobarbital sodium) decrease d the average PO2 in both Kupffer cells and the overall liver. The eff ects of perturbing the blood flow were studied by reversible blockage of the portal vein and hepatic artery in anesthetized mice; the PO2 in both Kupffer cells (measured with India ink) and in overall liver (me asured with LiPc) decreased with obstruction of the blood flow and ret urned toward normal with reperfusion. These results indicate that the PO2 in different locations in the liver can be significantly different under both normal conditions and after perturbation by either anesthe sia or ischemia. These results also demonstrate that EPR oximetry can provide sensitive measurements of PO2 in the liver in vivo under vario us conditions.