Molecular Pharmacology, Vol 19, 513-516, Copyright © 1981 by the American Society for Pharmacology and Experimental Therapeutics

A Fluorometric Method To Measure Sublobular Rates of Mixed-Function Oxidation in the Hemoglobin-Free Perfused Rat Liver

¹ Departments of Pharmacology and Anatomy, University of North Carolina School of Medicine, Chapel Hill, North Carolina 27514

A new fluorometric method has been developed to measure the relative rates of the 7-ethoxycoumarin O-deethylase activities in periportal and pericentral regions of the liver lobule. The method utilizes a pair of micro-light guides constructed from two strands of 80 µm-diameter glass optical fibers. The micro-light guides are placed in periportal and pericentral regions on the surface of the perfused liver. The increase in tissue fluorescence due to 7-hydroxycoumarin formation from 7-ethoxycoumarin is measured in periportal and pericentral regions by illuminating tissue with light at 360 ± 50 nm and measuring fluorescence at 450 ± 50 nm. Since the steady-state tissue fluorescence due to 7-hydroxycoumarin monitored with a large light guide was found to be directly proportional to the steady-state rate of 7-ethoxycoumarin O-deethylation, the sublobular fluorescence of 7-hydroxycoumarin measured by micro-light guides following infusion of 7-ethoxycoumarin allows one to estimate sublobular rates of the mixed-function oxidation of 7-ethoxycoumarin. The results indicate that the rate of 7-ethoxycoumarin O-deethylation is approximately twice as large in pericentral regions as in periportal areas of the liver.

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ACKNOWLEDGMENTS We thank Professor B. Chance for introducing us to tissue photometry and Dr. L. Reinke for helpful comments. The optical fiber was generously donated by Dr. W. P. Siegmund, Fiber Optics Division, American Optical Company, Southbridge, Mass. 01550.