Ultrastructural changes in hepatocytes of mice exposed to arsenic in drinking water.

Arsenic belongs to the important occupational and environmental agents which can cause damages to the liver by chronic exposure. In a long-term experimental (64 days) in mice the changes in liver cells due to arsenic were studied on the ultrastructural level. The qualitative and quantitative evaluation of the results obtained demonstrate two types of response. The first one was an acute reaction (maximum 4 days) characterized by enlargement of the surfaces of some inner membraneous structures of the hepatocytes (invaginations of the nuclear membrane and undulations of the mitochondrial surface) as well as by loss of glycogen. These changes receded gradually during the course of the experiment. The second type was characterized by a strikingly delayed change (maximum 32 days) represented by the occurrence of dense lamellar structures in the peroxisomes. Both types of response persisted till the termination of the experiment (64 days). The first type of response is considered to be a consequence of the direct toxic action of arsenic, the second one is interpreted as an expression of induced tolerance to arsenic of the organism.