Tissue thyroid hormone levels in critical illness.
BACKGROUND
Pronounced alterations in serum thyroid hormone levels occur during critical illness. T3 decreases and rT3 increases, the magnitudes of which are related to the severity of disease. It is unclear whether these changes are associated with decreased tissue T3 concentrations and, thus, reduced thyroid hormone bioactivity. PATIENTS AND STUDY QUESTIONS: We therefore investigated, in 79 patients who died after intensive care and who did or did not receive thyroid hormone treatment, whether total serum thyroid hormone levels correspond to tissue levels in liver and muscle. Furthermore, we investigated the relationship between tissue thyroid hormone levels, deiodinase activities, and monocarboxylate transporter 8 expression.


RESULTS
Tissue iodothyronine levels were positively correlated with serum levels, indicating that the decrease in serum T3 during illness is associated with decreased levels of tissue T3. Higher serum T3 levels in patients who received thyroid hormone treatment were accompanied by higher levels of liver and muscle T3, with evidence for tissue-specific regulation. Tissue rT3 and the T3/rT3 ratio were correlated with tissue deiodinase activities. Monocarboxylate transporter 8 expression was not related to the ratio of the serum over tissue concentration of the different iodothyronines.


CONCLUSIONS
Our results suggest that, in addition to changes in the hypothalamus-pituitary-thyroid axis, tissue-specific mechanisms are involved in the reduced supply of bioactive thyroid hormone in critical illness.
Peeters
Robin P
RP
Department of Internal Medicine, Erasmus University Medical Center, Rotterdam, The Netherlands.
van der Geyten
Serge
S
Wouters
Pieter J
PJ
Darras
Veerle M
VM
van Toor
Hans
H
Kaptein
Ellen
E
Visser
Theo J
TJ
Van den Berghe
Greet
G
D000368:Aged; D016638:Critical Illness; D005260:Female; D006801:Humans; D007328:Insulin / Q000627:therapeutic use; D007453:Iodide Peroxidase / Q000378:metabolism; D008099:Liver / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D027501:Monocarboxylic Acid Transporters; D018482:Muscle, Skeletal / Q000378:metabolism; D016032:Randomized Controlled Trials as Topic; D027981:Symporters; D014284:Triiodothyronine / Q000097:blood / Q000378:metabolism* / Q000627:therapeutic use; D014285:Triiodothyronine, Reverse / Q000378:metabolism
D007328:Insulin; D027501:Monocarboxylic Acid Transporters; C090735:SLC16A2 protein, human; D027981:Symporters; D014284:Triiodothyronine; D014285:Triiodothyronine, Reverse; D007453:Iodide Peroxidase