Changes in metabolism of TRH in euthyroid sick syndrome

Objective: The aim of this study was to examine the metabolism of a simple dose, intravenously administered TRH bolus of 200 mu g, in patients with eu thyroid sick syndrome (ESS). Patients and Methods: A TRH test was performed on ten ESS patients and ten controls upon admission (d1) and after recovery (d2), Blood samples were co llected at 0, 10, 20 and 30 min after TRH injection. We analyzed the Volume of distribution (V-d) the plasma clearance rate (PCR), the fractional clea rance rate (FCR), the half-life (t(1/2)) and the TSH response to the inject ion of TRH. Results: All patients had lower tri-iodothyronine (T-3) levels compared wit h controls (0.9 +/- 0.1 nmol/l vs 1.9 +/- 0.1 nmol/l; P < 0.0001; mean +/- S.D.: paired t-test). In addition, the V-d (16.7 +/- 5.9/l vs 30.6 +/- 0.6/ l: P < 0.0005) and PCR (2.0 +/- 0.80 l/min vs 3.3 +/- 0.25 l/min; P < 0.000 5) were found statistically lowered in patients than in controls, whereas F CR (0.119 +/- 0.01 per min vs 0.110 +/- 0.01 per min: P < 0.025) was found increased in patients as opposed to controls, The t(1/2) Of exogenously adm inistered TRH was increased in ESS compared with controls (7.2 +/- 0.7 min vs 6.3 +/- 0.6 min: P < 0.005). TSH response to TRH was found significantly repressed at 10, 20 and 30 min after TRH injection, On d2, these findings had reverted to normal and no changes regarding the kinetics of TRH and the response of TSH could be detected between patients and controls. Conclusions: The results demonstrate an impairment of TRH metabolism in ESS . The findings may suggest altered enzymatic activity, responsible for TRH degradation in states of acute ESS. These changes might be involved in the pathogenesis of ESS and represent part of an adaptive mechanism to this syn drome.