To investigate relationships between thyroid states and the cardiac endocrine 
system, we analyzed thyrotropin (TSH), thyroid hormone, plasma levels of 
interleukin-6 (IL-6) and brain natriuretic peptide (BNP) in 50 patients with 
chronic heart failure (CHF), in 30 patients with heart failure from acute 
myocardial infarction (AMI), and in 15 controls. Plasma levels of IL-6 and BNP 
in both CHF and AMI were significantly elevated, while free triiodothyronine 
(FT3) was significantly decreased compared to controls. FT3/free thyroxine (FT4) 
ratio was significantly decreased in CHF but not in AMI compared to controls. In 
CHF, diuretic treatment diminished circulating BNP but not IL-6, while diuretic 
treatment increased FT3/FT4 ratio. In AMI, FT3/FT4 ratio was significantly 
decreased 72 h compared to 12 h after the onset of AMI, while BNP and IL-6 were 
significantly increased 72 h compared to 12 h after the onset of AMI. In both 
CHF and AMI, BNP significantly correlated with FT4. On the other hand, 
significant correlations between IL-6 and FT3, and between IL-6 and FT3/FT4 
ratio were detected in AMI but not in CHF. This preliminary study suggests that 
IL-6, BNP and thyroid hormone reflect ventricular dysfunction in both acute and 
chronic heart failure, and that IL-6 significantly relates to circulating 
thyroid hormone in AMI but not in CHF.