INFLUENCE OF SLICE THICKNESS AND CULTURE CONDITIONS ON THE METABOLISMOF 7-ETHOXYCOUMARIN IN PRECISION-CUT RAT-LIVER SLICES

This study investigated the effects of some experimental variables on the rate of xenobiotic metabolism in precision-cut rat liver slices. L iver slices of 123 +/- 8 mu m (mean +/- SEM of six slices), 165 +/- 3 mu m, 238 +/- 6 mu m and 515 +/- 14 mu m thickness were prepared from male Sprague-Dawley rats, and incubated in RPMI 1640 medium in an atmo sphere of 95% O-2/5%, CO2 by using a dynamic organ culture system. Liv er slices of all thicknesses metabolised 10 mu M 7-ethoxycoumarin to t otal (free and conjugated) 7-hydroxycoumarin in a time-dependent manne r. The rate of 7-ethoxycoumarin metabolism was greatest in 165 mu m th ick slices and slowest in 515 mu m thick slices, being 2.74 +/- 0.19pm ol/minute/mg slice protein and 0.64 +/- 0.07pmol/minute/mg slice prote in, respectively. No marked effects on the rate of 7-ethoxycoumarin me tabolism in liver slices were observed either by changing the medium t o Earle's balanced salt solution (EBSS) or by changing the gas phase t o 95% air/5% CO2. Moreover, the perfusion of rat livers with EBSS at 2 -4 degrees C, prior to preparation of tissue cores, did not enhance 7- ethoxycoumarin metabolism in rat liver slices. In this study, the opti mal slice thickness was 175 mu m, with higher rates of 7-ethoxycoumari n metabolism being observed than with 250 mu m thick slices, which are often used for studies of xenobiotic metabolism. Variable results wer e obtained with slices of around 100-120 mu m thickness, which may be attributable to the ratio between intact hepatocytes and cells damaged by the slicing procedure in these very thin slices.