Abstract
To obtain detailed information on phenobarbital (PB)-induced cytochrome P-450 (P-450) increase and endoplasmic reticulum (ER) proliferation in hepatocytes, we estimated microphotometrically the amount of P-450 per unit cytoplasmic volume and morphometrically the area of ER per unit cytoplasmic volume in hepatocytes adjacent to the portal area or central venule (1 periportal or 1 perivenular cells) and in the second and third layers from the portal area or central venule (2, 3 periportal or 2, 3 perivenular cells) from mice injected with 35, 50, 100, or 150 mg/kg PB once a day for 3 days. By dividing the P-450 amount by the ER area, the number of P-450 molecules per unit ER area was also calculated. In 1 and 2, 3 perivenular cells, except for 2, 3 perivenular cells after injection of 150 mg/kg PB, the amount of P-450 increased with ER proliferation and the number of P-450 molecules in ER remained unchanged after injection of 50, 100, or 150 mg/kg PB. In 2, 3 periportal cells, however, the P-450 amount and the number of P-450 molecules in ER increased markedly without or with some ER proliferation after injection of 50, 100, or 150 mg/kg PB; the P-450 increase appears to be generally independent of ER proliferation. The 1 periportal cells are probably exceptional hepatocytes that usually did not respond to PB stimulation.