Induction of cytochrome P450 by phenobarbital in rat liver visualized by monoclonal antibody immunoelectron microscopy in situ.

A panel of murine monoclonal antibodies was produced against phenobarbital-inducible cytochrome P450-PB of rat liver in order to establish specific immunological tools for studying the induction process in situ by immunoelectron microscopy and in vitro by a novel ELISA. Antibody 573/64 was found to be useful for both approaches. The immunolabeling procedure with protein A-colloidal gold applied to Lowicryl K4M-embedded rat liver revealed the rough ER as the primary site of cytochrome P450-PB induction. This organelle showed the highest labeling density 12 h after administration of phenobarbital while after maximal enzyme induction at day 5 the labeling density was highest in the smooth ER. Maximal increase in cytochrome P450-PB was 21-fold by morphometric analysis and 15-fold by ELISA. In addition, the enzyme apparently does neither recycle through the Golgi apparatus nor is it degraded in lysosomes when maximally induced.