Ultrastructural changes in the liver after chronic exposure to methylmercury.

Adult male rats were injected daily with 1.0 mg/kg methylmercuric chloride for 5 weeks. Tissue samples from the liver were obtained at time intervals of 1, 2, 3, 4, 5, and 11 weeks for electron microscopic examination. A moderate accumulation of glycogen and proliferation of smooth endoplasmic reticulum was found in many hepatocytes after 1–2 weeks of intoxication. Swelling, pleomorphic, and degenerative changes of the hepatic mitochondria could be observed after the second week of methylmercury administration. After 3–5 weeks of intoxication, increased peribiliary accumulation of lysosomes, and large areas of focal cytoplasmic degradation were prominent pathological findings. Moderate accumulation of lipoprotein granules within dilated cisternae of the smooth endoplasmic reticulum and Golgi vesicle was observed in some hepatocytes after 5 weeks of continuous exposure to methylmercury. Large cytosegresomes containing various degenerating organelles were a frequent observation throughout the experimental period. Many of these cytosegresomes were being extruded into the sinusoidal spaces and engulfed by the Kupffer cells. At the eleventh week (6 weeks of recovery), various degenerative changes still could be found in some hepatocytes. Such long-lasting pathological changes in the liver are believed to be due to the effects of the residual and the recirculating mercury.