Use of epr oximetry with india ink to measure the po2 in the liver in vivo in mice

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Abstract
The partial pressure of oxygen (pO2) of the liver in vivo in unanesthetized mice was determined using electron paramagnetic resonance (EPR) oximetry with India ink. The EPR spectra were obtained using a low‐frequency (1.2 GHz) EPR spectrometer with a loop gap cavity resonator. The line width of the India ink used in this experiment was reversibly broadened by oxygen and was particularly sensitive to pO2 below 30 torr. After the administration of India ink into the tail vein, the India ink particles were taken up mainly by Kupffer cells in the liver and in part by phagocytes in the spleen. The pO2 measured in the normal liver was about 14 torr and was constant for the 2‐week experimental period. The pO2 decreased when measured at 1, 2, and 6 days after treatment with a hepatotoxin (carbon tetrachloride (CCI4)); within 2 weeks, it returned almost to the initial level. Measurements by EPR at sacrifice of controls and CCI4‐treated mice indicated that more than 90% of the India ink went to the liver; the spleen contained 4.7% of total amount in control mice and 8.8% in CCI4‐treated mice when measured 2 weeks after the treatment. These data indicate the usefulness of India ink for measuring the pO2 of the liver in vivo and that the pO2 in the Kupffer cells is decreased when the liver is damaged by CCI4.