The sequence of the structural changes in the endoplasmic reticulum (RER and SER) during the synthesis of drug-metabolizing enzymes in the liver.

Ingestion or administration of lipid soluble drugs, e.g. phenobarbital to human or animal, induces the liver cells to produce drug-metabolizing enzymes. The process of enzyme synthesis which takes place in the endoplasmic reticulum, is a sequential event and can be divided into three stages as seen on the electron micrographs. The first stage is the period of increased production of the rough endoplasmic reticulum (RER) and the hypertrophy of the same in the cytoplasm. During the period of RER production, the various drug metabolizing enzymes are also being synthesized in the RER. After the completion of enzyme synthesis. The probable 'saturation' of the RER membranes with the enzymes, the RER begins to shed its attached ribosomes at specific points on the membrane, hitherto designated as conversion points, to become the smooth endoplasmic reticulum (SER) with the same attached enzymes. The new SER accumulates at distinct areas in the cytoplasm also designated as RER leads to SER conversion centres. Each conversion centre consists of a central core of net-like SER tubules surrounded by finger-like tubules of RER which converge radially on the SER core. There are membrane continuities between the SER in the core and the peripherally converging RER. The conversion centres are randomly distributed in the cytoplasm. They are neither related to any organelle nor polarised in respect to the poles of the cell.