Triiodothyronine supplementation in a sheep model of intensive care.

Triiodothyronine (T3) concentrations in plasma decrease during acute illness and it is unclear if this contributes to disease. Clinical and laboratory studies of T3 supplementation in disease have revealed little or no effect. It is uncertain if short term supplementation of T3 has any discernible effect in a healthy animals. Observational study of intravenous T3 (1 µg/kg/h) for 24 h in a healthy sheep model receiving protocol-guided intensive care supports (T3 group, n=5). A total of 45 endpoints were measured including hemodynamic, respiratory, renal, hematological, metabolic and endocrine parameters. Data were compared with previously published studies of sheep subject to the same support protocol without administered T3 (No T3 group, n=5). Plasma free T3 concentrations were elevated 8-fold by the infusion (pmol/l at 24 h; T3 group 34.9±9.9 vs. No T3 group 4.4±0.3, P<0.01, reference range 1.6 to 6.8). There was no significant physiological response to administration of T3 over the study duration. Supplementation of intravenous T3 for 24 h has no physiological effect on relevant physiological endpoints in healthy sheep. Further research is required to understand if the lack of effect of short-term T3 may be related to kinetics of T3 cellular uptake, metabolism and action, or acute counterbalancing hormone resistance. This information may be helpful in design of clinical T3 supplementation trials.