The induction of liver microsomal proteins by 3-methylcholanthrene in rats of different age, sex and strain.

The treatment of male and female adult and male and female immature rats with 3-methylcholanthrene results in increases in the intensity of two liver microsomal protein bands separated by sodium dodecyl sulphate-polyacrylacrylamide gel electrophoresis. The induced protein species have estimated molecular weights of about 55 000 and 52 500. The time course of the induction of these species has been followed in a semi-quantitative manner. In immature rats an additional band, corresponding to a protein species with a molecular weight of about 43 000, is also increased by 3- methylcholanthrene treatment. In male adult rats exclusively, treatment with 3-methylcholanthrene also results in a decrease in the intensity of a band corresponding to a protein species of about 51 000. The appearance of this band in the liver microsomal fraction of adult male rats occurs following sexual maturation and its presence represents a significant difference in the microsomal proteins between male and female rats; this protein is not detected in younger rats or in female rats at any age. These findings are discussed in terms of their possible relevance to the cytochrome P-450 content of the endoplasmic reticulum of rat hepatocytes.