Cardiac recovery from pressure overload is not altered by thyroid hormone status in old mice

Thyroid hormones (TH) are known to have various effects on the cardiovascular system. However, the impact of TH levels on preexisting cardiac diseases are still unclear. Pressure overload due to arterial hypertension or aortic stenosis and aging are major risk factors for the development of structural and functional abnormalities and subsequent heart failure. Here, we assessed the sensitivity to altered TH levels in aged mice with maladaptive cardiac hypertrophy and cardiac dysfunction induced by transverse aortic constriction (TAC). Mice at the age of 12 months underwent TAC and after induction of left ventricular pressure overload, received T4 or anti-thyroid medication in the drinking water over the course of 4 weeks. T4 excess or deprivation in older mice had no or only very little impact on cardiac function (fractional shortening), cardiac remodeling (cardiac wall thickness, heart weight, cardiomyocyte size, apoptosis and interstitial fibrosis) and mortality. This is surprising, because T4 excess or deprivation had significantly changed the outcome after TAC in young 8-week-old mice. In summary, our study shows that low and high TH availability have little impact on cardiac function and remodeling in older mice with preexisting pressure induced cardiac damage. This suggests that even though cardiovascular risk is increasing with age, the response to TH stress may be dampened in certain conditions.