Alterations in cardiac contractility and gene expression during low-T3 syndrome: prevention with T3

Am J Physiol. 1997 Nov;273(5):E951-6. doi: 10.1152/ajpendo.1997.273.5.E951.

Abstract

The low-T3 syndrome is a metabolic response resulting in a decreased serum triiodothyronine (T3) concentration that has uncertain effects on thyroid hormone-responsive gene expression and function. We measured cardiac myocyte gene expression and cardiac contractility in young adult female rats using chronic calorie deprivation as a model of the low-T3 syndrome. Sarcoplasmic reticulum calcium adenosinetriphosphatase (SERCA2) and myosin heavy chain (MHC) isoform mRNA content were measured after 28 days on a 50% calorie-restricted diet (low T3) with or without T3 treatment (6 micrograms.kg body wt-1.day-1). The low-T3 animals had decreased maximal rates of contraction (-13%; P < 0.05) and relaxation (-18%; P < 0.05) compared with the control and the T3-treated groups. There was a 21% (P < 0.05) increase in left ventricular (LV) relaxation time in the low-T3 animals vs. both control and T3-treated groups. The LV content of the SERCA2 mRNA was decreased significantly (37%) in the low-T3 rats and was increased (P < 0.05) with T3 treatment vs. controls. The alpha-MHC mRNA isoform decreased in the low-T3 animals but was unchanged in the T3-treated animals. T3 supplementation normalized both cardiac function and phenotype of calorie-restricted animals, suggesting a role for the low-T3 syndrome in the pathophysiological response to calorie restriction.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Body Weight / drug effects
  • Calcium-Transporting ATPases / biosynthesis*
  • Diet, Reducing
  • Euthyroid Sick Syndromes / drug therapy
  • Euthyroid Sick Syndromes / metabolism
  • Euthyroid Sick Syndromes / physiopathology*
  • Female
  • Gene Expression Regulation / drug effects
  • Gene Expression Regulation / physiology*
  • Heart / drug effects
  • Heart / physiology
  • Heart / physiopathology*
  • Hypothyroidism / physiopathology
  • Myocardial Contraction* / drug effects
  • Organ Size / drug effects
  • Rats
  • Rats, Sprague-Dawley
  • Thyroxine / blood
  • Transcription, Genetic / drug effects
  • Triiodothyronine / blood
  • Triiodothyronine / pharmacology*
  • Triiodothyronine / therapeutic use
  • Ventricular Function, Left / drug effects
  • Weight Gain

Substances

  • Triiodothyronine
  • Calcium-Transporting ATPases
  • Thyroxine