title: Triiodothyronine depresses the NAD-linked glycerol-3-phosphate dehydrogenase activity of cultured neonatal rat heart cells.
abstract: The activity of NAD-linked alpha-glycerol-3-phosphate dehydrogenase (NAD-G3PDH; EC 1.1.1.8) was depressed by 35% when the thyroid hormone 3,3',5-triiodo-L-thyronine (20 micrograms/liter) was added to the serum-free, hormonally supplemented medium of cultured neonatal rat heart cells. The degree of depression was greater (65%) when the medium contained normal serum levels of hydrocortisone and insulin. There is a dramatic inverse dose-response relationship between triiodothyronine levels and NAD-G3PDH activity. The classic elevation by thyroid hormones of the FAD-linked alpha-glycerol-3-phosphate dehydrogenase (FAD-G3PD; EC 1.1.99.5) was observed concurrently. The medium-glucose depletion rate in triiodothyronine-free cells was depressed 32% through 11 days-in-culture, indicating reduced glycolytic activity. The activities of nine other metabolically important enzymes which were measured during this study, including hexokinase, glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, phosphofructokinase, pyruvate kinase, malate dehydrogenase, NAD-isocitrate dehydrogenase, NADH cytochrome c reductase, and succinic cytochrome c reductase, did not respond to varying triiodothyronine concentrations.
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D002478:Cells, Cultured; D005993:Glycerolphosphate Dehydrogenase / Q000037:antagonists & inhibitors*; D009206:Myocardium / Q000201:enzymology*; D009243:NAD / Q000378:metabolism; D051381:Rats; D014284:Triiodothyronine / Q000494:pharmacology*
chemical_list: D014284:Triiodothyronine; D009243:NAD; D005993:Glycerolphosphate Dehydrogenase