Direct effect of thyroid hormones on glucose oxidation by isolated rat cardiac myocytes

Abstract

The incubation of isolated heart muscle cells in phosphate buffered saline in the presence of triiodothyronine (10 −5 to 10 −9 m) stimulated the oxidation of 14C-U-glucose. L-thyroxine was equally effective in stimulating glucose oxidation, while the D-isomer was ineffective. No stimulation of oxidation of either 14C-U-labelled lactate or 14C-1 labelled octanoate was observed. There was no preferential oxidation of the C-1 carbon versus the C-6 carbon of glucose. Examination of the glycolytic intermediates of triiodothyronine treated cells showed a significant decrease in the level of fructose-6-phosphate and a slight increase in the level of fructose-1, 6-diphosphate. From these results it is postulated that the observed effect is due to a stimulation of phosphofructokinase.