Alterations in the fine structure of hepatocytes in hyperthyroid rats.

Ultrastructural investigation of liver from ten radiothyroidectomized adult male albino rats, made hyperthyroid by administration of desiccated thyroid for eight to ten weeks, revealed changes in hepatic organelles, but no differences between centrilobular, midzonal and periportal hepatocytes of a single lobule. The mitochondria were enlarged with an increase in matrix density, but no increase in number of mitochondria or alterations in membranes or cristae was observed. The smooth endoplasmic reticulum appeared slightly increased and dilated in treated rats, while stacked cisternae of the rough endoplasmic reticulum were seldom seen. Large vacuoles, which often contained follicular material and frequently opened into the spaces of Disse, were observed at the periphery of hepatocytes. The vacuoles may arise from invaginations of the cell membrane along these spaces to increase the surface area and to act as channels for liver metabolites. Moreover, in hyperthyroid rats hepatic glycogen was uniformly depleted. Whether these changes were a primary effect of thyroid hormone or secondary to metabolic alterations is unclear.