title: Thyroid hormone regulation of cardiac bioenergetics: role of intracellular creatine.
abstract: The effect of thyroid hormone (T(3)) on the content of myocardial creatine (Cr), Cr phosphate (CrP), and high-energy adenine nucleotides and on cardiac function was examined. In the hearts of control and T(3)-treated rats perfused in vitro, while "low" and "high" contractile work was performed, T(3) treatment resulted in a approximately 50% reduction in CrP, Cr, total Cr content (Cr + CrP), and in the CrP-to-Cr ratio. In addition, there was a slight fall in myocardial content of ATP and a large rise in calculated free ADP (fADP), resulting in a significant decrease in the ATP-to-fADP ratio in the hearts of hyperthyroid compared with euthyroid rats. Moreover, there was a substantial decrease in the level of ATP in hearts of T(3)-treated rats under high work conditions. Importantly, the ratio of cardiac work to oxygen consumption was not altered by thyroid status. Treatment with T(3) also resulted in an almost threefold reduction in the content of Na(+)/Cr transporter mRNA in the ventricular myocardium and skeletal muscle but not in the brain. We conclude with the following: 1) changes in the expression of the Na(+)/Cr transporter mRNA correlate with Cr + CrP in the myocardium; 2) hearts of hyperthyroid rats contain lower levels of ATP and higher levels of fADP under both low and high work conditions but no reduction in efficiency of work output; and 3) the reduction in Cr and ATP in hearts of hyperthyroid rats may be the basis for the reduced maximal work capacity of the hyperthyroid heart.
authors.affiliation: Department of Medicine and Physiology and Biophysics, Case Western Reserve University, Cleveland, Ohio 44106-4951, USA.
authors.forename: Marcia Silva
authors.initials: MS
authors.lastname: Queiroz
authors.forename: Yvonne
authors.initials: Y
authors.lastname: Shao
authors.forename: Deborah A
authors.initials: DA
authors.lastname: Berkich
authors.forename: Kathryn F
authors.initials: KF
authors.lastname: Lanoue
authors.forename: Faramarz
authors.initials: F
authors.lastname: Ismail-Beigi
mesh_terms: D000244:Adenosine Diphosphate / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001794:Blood Pressure / Q000502:physiology; D001835:Body Weight / Q000187:drug effects; D001921:Brain / Q000378:metabolism; D003401:Creatine / Q000378:metabolism*; D004734:Energy Metabolism / Q000187:drug effects / Q000502:physiology*; D006321:Heart / Q000187:drug effects / Q000502:physiology; D006339:Heart Rate / Q000502:physiology; D006980:Hyperthyroidism / Q000378:metabolism*; D066298:In Vitro Techniques; D007424:Intracellular Fluid / Q000378:metabolism; D008297:Male; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism; D018482:Muscle, Skeletal / Q000378:metabolism; D009206:Myocardium / Q000378:metabolism*; D009929:Organ Size / Q000187:drug effects; D010101:Oxygen Consumption / Q000187:drug effects; D010725:Phosphocreatine / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D013599:Systole / Q000502:physiology; D014284:Triiodothyronine / Q000494:pharmacology*
chemical_list: D026901:Membrane Transport Proteins; D012333:RNA, Messenger; C080679:creatine transporter; D010725:Phosphocreatine; D014284:Triiodothyronine; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D003401:Creatine