The effects of exertional heat stroke (ExHS), with or without acute renal failure (ARF), on thyroid hormone metabolism were investigated. Eighteen ExHS patients were recruited and divided into two groups based on the presence or absence of ARF. Eleven age-matched healthy subjects served as a control group. Serum values of T3, T4, TSH, free T4 (FT4), rT3, and sulfated T3 (T3S) were measured in these groups during the acute and recovery stages of ExHS. Serum T3, T4, and FT4 levels were reduced, with reciprocal increases in rT3 and T3S levels as the severity of ExHS increased. The following mean levels of thyroid hormones were found (controls vs. ExHS without ARF vs. with ARF): T3, 1514 vs. 1164 vs. 393 pmol/L (P <0.05 each); T4, 97 vs. 79 vs. 49 nmol/L (P = NS and P <0.05, respectively); FT4, 20.5 vs. 19.5 vs. 19.0 pmol/L (P = NS each); rT3, 371 vs. 617 vs. 805 pmol/L (P <0.05 and P = NS, respectively); and T3S, 30.1 vs. 34.2 vs. 71.1 pmol/L (P = NS and P <0.05, respectively). The serum TSH levels were not significantly different among the three groups. Significantly negative correlations were found between serum creatinine and T3 (r = 0.75; P <0.001) and T4 levels (r = -0.65; P <0.001), whereas no relationship was noted between serum creatinine and rT3 values (r = 0.11; P > 0.05). In contrast, a correlation was observed between serum glutamic pyruvic transaminase and rT3 (r = 0.45; P <0.01). Thyroid function tests returned to normal after patients recovered. In conclusion, our results show that patients suffering from ExHS, with or without ARF, displayed altered serum thyroid function in proportion to the severity of their condition. No significant changes in serum levels of rT3 were observed between the two groups, whereas a positive relationship was observed between serum rT3 and serum glutamic pyruvic transaminase values, suggesting that the changes in serum rT3 levels were more dependent on extrarenal illness than on renal disease per se. The moderate increase in serum T3S levels found in patients suffering from both ExHS and ARF may represent a decrease in tissue 5'-monodeiodinase activity as found in other nonthyroidal illnesses. A return of serum thyroid function tests to normal values after recovery from ExHS suggests that the low T3 state may play a protective role to prevent undesirable catabolic effects. Replacement therapy is thus not recommended.
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