Critical illness
alters the activity of enzymes that metabolize thyroid hormones
(November 2003)
The background of the study. Patients
with severe nonthyroidal illness have many abnormalities in thyroid
function, most often low serum triiodothyronine (T3) concentrations
and high serum reverse triiodothyronine (rT3) concentrations. (T3
is an active hormone and rT3 is inactive.) These changes are caused
by changes in the activity of one or more of the three deiodinase
enzymes that remove iodine atoms from thyroxine (T4), T3, or rT3.
Serum T4, T3, and rT3 and the activity of the deiodinases in liver
and muscle were measured in patients who died during an acute illness.
How the study was done. Serum or
biopsies of liver or skeletal muscle were obtained from 80 patients
who died of cardiovascular collapse, sepsis, multiple organ failure,
or severe brain damage. Serum T4, T3, rT3, and thyrotropin (TSH)
were measured, and the activity of the deiodinases was determined
by measuring the formation of iodine-125 in tissue homogenates incubated
with iodine-125-labeled T4, T3, or rT3.
The results of the study. The patients
had low serum T4 and T3 values, high serum rT3 values, and low serum
TSH values. Liver deiodination of T4 to T3 was decreased, and liver
and muscle deiodination of T4 to rT3 was increased. Hepatic T4 to
T3 deiodinating activity was lowest in the patients who died from
cardiovascular collapse, and highest (and normal) in the patients
who died from severe brain damage. This activity was low in patients
with acute renal failure, and was negatively correlated with serum
creatinine concentrations in all patients.
The conclusions of the study. Critically
ill patients have alterations in the activity of the deiodinating
enzymes that activate and inactivate T4. Whether these changes are
beneficial or harmful is not known.
The original article. Peeters RP,
Wouters PJ, Kaptein E, van Toor H, Visser TJ, Van den Berghe G.
Reduced activation and increased inactivation of thyroid hormone
in tissues of critically ill patients. J Clin Endocrinol Metab 2003;88:3202-11.
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