THE HEART AND ENDOCRINOLOGY 

Minerva Endocrinologica 2004 September;29(3):139-50

Copyright © 2004 EDIZIONI MINERVA MEDICA

language: English

Thyroid hormone and cardiovascular system

Danzi S., Klein I.

Thyroid hormone is an important regulator of cardiac function and cardiovascular hemodynamics. Triiodothyronine, (T3), the physiologically active form of thyroid hormone, binds to nuclear receptor proteins and mediates the expression of several important cardiac genes, inducing transcription of the positively regulated genes including a-myosin heavy chain (MHC) and the sarcoplasmic reticulum calcium ATPase. Negatively regulated genes include b-MHC and phospholamban, which are down regulated in the presence of normal serum levels of thyroid hormone. T3 mediated effects on the systemic vasculature include relaxation of vascular smooth muscle resulting in decreased arterial resistance and diastolic blood pressure. In hyperthyroidism, cardiac contractility and cardiac output are enhanced and systemic vascular resistance is decreased, while in hypothyroidism, the opposite is true. Patients with subclinical hypothyroidism manifest many of the same cardiovascular changes, but to a lesser degree than that which occurs in overt hypothyroidism. Cardiac disease states are sometimes associated with the low T3 syndrome. The phenotype of the failing heart resembles that of the hypothyroid heart, both in cardiac physiology and in gene expression. Changes in serum T3 levels in patients with chronic congestive heart failure are caused by alterations in thyroid hormone metabolism suggesting that patients may benefit from T3 replacement in this setting.