Abstract
1. Changes in the structure and function of the rough-surfaced endoplasmic reticulum of the rat liver as deduced by electron microscopy, polysome analysis and the amino acid-incorporating activity of microsome fractions have been followed at various time-intervals after a single intraperitoneal dose of the hepatocarcinogen 4-dimethylaminoazobenzene. 2. The earliest effect observed was detachment of polysomes and disorganization and vesiculation of the cisternae of the rough-surfaced endoplasmic reticulum. This occurred after 6hr. 3. Subsequent to this was a phase of polysome disaggregation accompanied by impaired amino acid-incorporating activity by microsomes together with a much enhanced stimulating effect of polyuridylic acid on amino acid uptake. This reached a maximum at 24hr. 4. By 40hr. polysomes had re-formed and the amino acid-incorporating activity, together with the polyuridylic acid effect, were similar to those in controls. 5. It was not until 112hr. that something like the normal structure of the rough-surfaced endoplasmic reticulum was re-established. 6. It is not yet possible to relate these changes specifically with the process of azo-dye carcinogenesis.