The Role of the Alpha-Glycerophosphate Cycle in the Control of Carbohydrate Oxidation in Cardiac Tissue and in the Mechanism of Action of Thyroid Hormone

摘要

The hypothesis that thyroid hormone increases the oxidation of extramitochondrial DPNH by stimulating the activity of mitochondrial alpha-glycerophosphate dehydrogenase and thereby accelerating the rate of operation of the alpha-glycerophosphate cycle was studied utilizing isolated, perfused rat hearts. Lactate, pyruvate, and glucose plus insulin were perfused individually through hearts matched to control hearts of the same weight from hyperthyroid and hypothyroid rats and the observed uptakes of the substrates were corrected for differences in heart rates. Hyperthyroid hearts showed a 300% increase and hypothyroid hearts an 80% decrease in mitochondrial alpha-glycerophosphate dehydrogenase specific activity. The thyroid status of the animals had no effect on the rate of uptake of pyruvate from the perfusate. On the basis of triose uptake during perfusion with glucose plus insulin, glucose uptake was the same as pyruvate uptake in control hearts, was unaffected by hyperthyroidism, and was increased slightly in hypothyroidism. The thyroid status of the animals had no effect on the cardiac tissue concentration of alpha-glycerophosphate, dihydroxyacetone phosphate, lactate, pyruvate, or DPN+, but hyperthyroid hearts had a higher concentration of DPNH than control hearts. (Author)