title: A phosphorus-31 nuclear magnetic resonance study of effects of altered thyroid state on cardiac bioenergetics.
abstract: We have used 31P nuclear magnetic resonance (NMR) techniques to characterize bioenergetic changes in the Langendorff-perfused rat heart accompanying alterations in thyroid state. Cytosolic phosphocreatine and inorganic phosphate concentrations changed significantly in both the hypo- and hyperthyroid groups compared to controls; the calculated phosphorylation potential [( ATP]/[ADP][Pi]) increased by 60% in hypothyroidism and decreased by 60% in hyperthyroidism relative to the euthyroid value of 47 X 10(3) M-1. Creatine phosphokinase (CPK) and mitochondrial ATP synthase rates were measured in the intact tissue using a saturation-transfer NMR method. There were no significant differences in the measured fluxes through the CPK reaction among the three groups (4.24 +/- 1.00 mM X sec-1 for the euthyroid group). Although O2 consumption increased by 46% in hearts from hyperthyroid animals, no change in the measured mitochondrial ATP synthase flux was observed compared to the euthyroid flux of 1.05 +/- 0.11 mM X sec-1. These results suggest that the apparent in situ P/O ratio of mitochondria in hearts from hyperthyroid animals is reduced relative to that in euthyroid controls.
authors.forename: J M
authors.initials: JM
authors.lastname: Keogh
authors.forename: P M
authors.initials: PM
authors.lastname: Matthews
authors.forename: A M
authors.initials: AM
authors.lastname: Seymour
authors.forename: G K
authors.initials: GK
authors.lastname: Radda
mesh_terms: D025181:ATP Synthetase Complexes; D000244:Adenosine Diphosphate / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D006332:Cardiomegaly / Q000503:physiopathology; D003402:Creatine Kinase / Q000378:metabolism; D004734:Energy Metabolism; D006980:Hyperthyroidism / Q000503:physiopathology*; D007037:Hypothyroidism / Q000503:physiopathology*; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D009097:Multienzyme Complexes / Q000378:metabolism; D009206:Myocardium / Q000201:enzymology*; D010101:Oxygen Consumption; D010477:Perfusion; D010710:Phosphates / Q000378:metabolism; D010725:Phosphocreatine / Q000378:metabolism; D010759:Phosphorus Isotopes; D010770:Phosphotransferases / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D009097:Multienzyme Complexes; D010710:Phosphates; D010759:Phosphorus Isotopes; D010725:Phosphocreatine; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D010770:Phosphotransferases; D003402:Creatine Kinase; D025181:ATP Synthetase Complexes