[Studies on circulating interleukin-6 and thyroid functions in acute myocardial infarction]

The euthyroid sick syndrome is reported to exist in acute myocardial infarction(AMI). Previous reports showed serum levels of triiodothyronine(T3) are low and thyroid stimulating hormone(TSH) is normal or subnormal levels in patients with AMI. However, the mechanism of altered thyroid hormone metabolism is unknown. Interleukin-6(IL-6) is reported to be a key role in the pathogenesis of AMI and euthyroid sick syndrome. We measured circulating TSH, free T3(FT3), free thyroxine (FT4), IL-6, soluble IL-6 receptor, soluble transducing 130-kD glycoprotein, atrial natriuretic peptide(ANP) and brain natriuretic peptide in 25 patients and 32 healthy subjects. Circulating FT3 levels in patients with AMI became lower than in control group(p < 0.05). IL-6 levels were significantly(p < 0.05) higher than those of healthy subjects. The peak levels of IL-6 was 30.5 +/- 46.9 pg/ml at 25-27 hours(the first peak) and 64.4 +/- 24.6 pg/ml at 70-72 hours(the second peak). FT3 was negatively related to IL-6(p < 0.05) and hANP(p < 0.05) in patients with AMI. These results indicate that the lower levels of FT3 show the greater severity of AMI. We conclude that euthyroid sick syndrome occurs in patients with AMI and euthyroid sick syndrome may regulated by IL-6 through suppressed of thyroid function.