Variations in immunoreactivity for phenobarbital- and 3-methylcholanthrene-inducible cytochromes P-450, and NADPH-cytochrome P-450 reductase in rat liver over twenty-four hours.

To reveal distribution patterns of phenobarbital- and 3-methylcholanthrene-inducible cytochromes P-450 (PB and MC) and NADPH-cytochrome P-450 reductase (P-450red) within the liver acinus of untreated rats, and their variations over 24 h, hepatic samples were examined by immunohistochemistry and image-analyzer at evenly spaced six time points over 24 h. When examined in semi-thin sections obtained from Epon-embedded, freeze-dried, and paraformaldehyde vapor-phase fixed materials, the immunoreactivity for these enzymes showed different distribution patterns within the liver acinus. Immunodeposits for PB were predominantly distributed in perivenous hepatocytes, whereas those for MC and P-450red were slightly more intense in periportal hepatocytes at each time point. The immunoreactivity for PB and MC in both perivenous and periportal hepatocytes increased during the dark period, peaking early in the light period. These variations coincide well with our previous morphometric results (Uchiyama and Asari, 1984); the volume and surface densities of rough endoplasmic reticulum (rER) in hepatocytes increased during the dark period. On the other hand, weak fluctuation was demonstrated in the immunoreactivity for P-450red in hepatocytes of both zones. These results suggest that PB and MC are retained in rER rather than smooth endoplasmic reticulum (sER) of hepatocytes obtained from untreated rats. These enzymes in sER may be short in their half-life spans.