Biochemical and stereological analysis of rat liver mitochondria in different thyroid states

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Abstract
The concentrations of the inner mitochondrial membrane markers cardiolipin and cytochrome a were measured in liver homogenates and in purified mitochondria after thyroxine [T4] administration to thyroidectomized and normal rats. The biochemical results were correlated with stereological electron micrographic analyses of hepatocytes in liver sections, and of isolated mitochondrial pellets. There were progressive and parallel increases in homogenate and mitochondrial cardiolipin concentration and in mitochondrial cytochrome a concentration, after administration of 20 .mu.g of T4 on alternate days to thyroidectomized rats, and of 300 .mu.g on alternate days to normal rats. EM measurements showed marked differences in the shape of the mitochondria and in the number of cristae in different thyroid states. Hypothyroid mitochondria were shorter and wider than controls, and hyperthyroid mitochondria were longer but of similar width. Mitochondrial volume per unit cell volume was virtually unchanged in hypo- and hyperthyroid animals. The most striking changes were a decrease in the area of the inner membrane plus cristae in thyroidectomized rats and a substantial increase in membrane area after T4 administration. The biochemical and electron micrographic results indicate that, in rat liver, thyroid hormone administration leads to a selective increase in the relative amount of mitochondrial inner membranes, with little or no change in the mitochondrial volume per unit cell volume, or in total mitochondrial protein per unit total cell protein.