One-year time-sequence inhalation toxicity study of vinyl chloride in rats. III. Morphological changes in the liver.

Wistar rats were exposed to atmospheres containing 0 (control) or 5000 ppm vinyl chloride monomer (VCM), 7 h/day, 5 days/week, for a period of 52 weeks. After 4, 13, 26 and 52 weeks each time 10 rats/sex/group were killed and subjected to extensive examinations. The present paper describes the morphological changes found in the liver. The major parenchymal changes comprised swelling and malformation of mitochondria, an increased amount of smooth endoplasmic reticulum, necrosis, nuclear and cellular polymorphism of hepatocytes, "foci of cellular alteration", neoplastic nodules and hepatocellular carcinomas. A reduced glucose-6-phosphatase activity in hepatocytes and a strong sinusoidal activity of alkaline phosphatase were found within "foci of cellular alteration". The non-parenchymal alterations included focal dilatation of sinusoids, focal proliferation of atypical sinusoidal cells and multicentric angiosarcomas. The effects of VCM on the hepatic parenchyma seemed to precede those on the hepatic stroma.