Cytochrome P-450 distribution in rat liver and the effect of sodium phenobarbitone administration

A microspectrophotometric method for assaying cytochrome P-450 in fresh 24 micrometer unfixed cryostat sections of rat liver has been developed. When used to assay this cytochrome in sections of microsomal preparations it has yielded results equivalent to those obtained by the conventional spectrophotometric assay of the same preparations. Random measurements made throughout sections of liver have given mean values for cytochrome P-450 concentrations which are twice those measured in microsomes prepared from the livers of the same animals (not corrected for the yield in the homogenate). Measurements of the cytochrome P-450 content of liver cells by the microspectrophotometric method show that in liver from male Wistar rats, cells nearer to the central veins contain up to twice as much cytochrome P-450 as those nearer to the portal tract (mean cell concentrations of 26.4 (+/-4.4) mumol/l and 17.5 (+/-3.0) mumol/l respectively). In the livers from similar rats, killed at the same time, but which has received 1 mg/ml sodium phenobarbitone in their drinking water for one week, the cells near the central vein contained up to five times as much cytochrome P-450 as those near the portal tract (mean cell concentrations of 77.3 (+/-25.0) mumol/l and 28.3 (+/-9.6) mumol/l respectively). The results show a selective increase in cytochrome P-450 content by the cells in the centrilobular region after treatment with sodium phenobarbitone and a smaller increase by some of the cells in the periportal region.