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Thyroid hormone regulation of mitochondrial alpha-glycerophosphate dehydrogenase in liver and hepatoma.

The effect of thyroid hormone in rats upon the induction of mitochondrial α-glycerophosphate dehydrogenase (LM-GPDH) has been studied in normal liver, in Novikoff hepatoma, in Morris hepatoma 7800, and in host liver of animals bearing Novikoff or Morris hepatomas. Enzyme activities were determined both before and 48 hr after a single i.p. injection of l-triiodothyronine (T3), 100 µg/100 g body weight. In livers of rats bearing the rapidly growing Novikoff hepatoma, basal enzyme activity is increased 75% over levels in nontumor-bearing controls. By contrast, hepatic enzyme activity in rats bearing the more slowly growing Morris hepatoma does not differ from control levels. In normal animals, administration of T3 greatly increases activity of LM-GPDH. In livers of animals bearing either Novikoff or Morris hepatomas, enzyme activity after administration of T3 is similar to levels obtained in livers of normal animals similarly treated.

The activity of LM-GPDH in Novikoff hepatoma, expressed per mg mitochondrial protein, is considerably higher than in liver, and cannot be induced by T3. In the Morris hepatoma, basal activity is similar to that of normal liver, and is increased 2-fold by T3. The present study, therefore, indicates that induction of LM-GPDH by thyroid hormone is not demonstrable in the Novikoff hepatoma, is diminished but present in the Morris hepatoma 7800, and is unimpaired in liver of rats bearing either tumor.