Upregulation of thyroid hormone receptor β1 and β2 messenger RNA in the myocardium of dogs with dilated cardiomyopathy or chronic valvular disease

Abstract

Objective - To investigate whether expression of thyroid hormone receptor (TR) messenger RNA (mRNA) is changed in the myocardium of dogs with heart failure. Animals - 21 dogs. Procedure - Concentrations of TR α2, β1, and β2 mRNA in the myocardium were determined for clinically normal dogs (n = 7) and dogs with heart failure caused by dilated cardiomyopathy (DCM; 7) or chronic valvular disease (CVD; 7). Concentrations were quantified by use of reverse transcription-polymerase chain reaction and ELISA. Results - The ratio of expression of TR α2, β1, and β2 mRNA was typically 100:10:1. Differences in concentration of TR α2 mRNA among the 3 groups of dogs were not detected, but concentrations of TR β1, and β2 mRNA were greater in diseased myocardium. Thyroid hormone receptor β1, mRNA was upregulated approximately threefold, and TR β2 mRNA was upregulated approximately eightfold in myocardium of dogs with DCM and CVD, compared with clinically normal dogs. There was no difference in TR β1, and β2 mRNA upregulation between dogs with DCM and CVD. Conclusions and Clinical Relevance - Altered regulation of transcription of the TR β gene may be one facet of the myocardial phenotype in heart failure. Because this phenotypic response did not differ on the basis of cause (DCM vs CVD), it appears to be a secondary effect of heart failure and the alteration in metabolism of thyroid hormone. Treatment of dogs with heart failure with thyroid hormone or thyroid hormone analogues may improve cardiac performance.