..Incubation of hypothalamic homogenates with [125I]T4 as described in Materials and Methods resulted in a 30 to 50% conversion of the substrate to [125I]rT3. Reverse T3 production was inhibited more than 80% by addition of 0.1 ��M T3 to the incubation mixture, confirming that this represents D3 activity. D3 activity was not significantly different selleck chemical Ceritinib but tended to be higher in chronically ill rabbits (prolonged ill rabbits 1.63 �� 0.45 fmol/min/mg protein vs. healthy controls 1.24 �� 0.34; P = 0.14).Expression levels of thyroid hormone transporters MCT10 (P = 0.04) and OATP1C1 (P = 0.002) were significantly increased in the hypothalamus of prolonged ill animals (Figure (Figure4a).4a). There was no change in MCT8 gene expression (Figure (Figure4a4a).

Figure 4Relative mRNA expression of thyroid hormone transporters and thyroid hormone receptors measured in hypothalamus of healthy control and prolonged ill rabbits. (a) Thyroid hormone transporters measured were MCT8, MCT10 and OATP1C1 and (b) thyroid hormone …Hypothalamic TR��1, TR��2, TR��1 and TR��2 expression was not significantly different in prolonged ill animals as compared with healthy controls (Figure (Figure4b4b).In prolonged ill rabbits, we measured a 40% reduction in hypothalamic T4 content as compared with healthy rabbits (P = 0.03, Figure Figure5).5). T3 content was not significantly different between the two groups, but tended to be lower in the critically ill animals (P = 0.17, Figure Figure55).Figure 5Local thyroid hormone concentrations in hypothalamus of healthy control (n = 10) and prolonged ill rabbits (n = 11).

Data are expressed as mean �� standard deviation. TT3 = Total T3; TT4 = Total T4DiscussionProlonged critical illness is hallmarked by reduced TRH gene expression in the face of low circulating T3 levels. In our animal model of prolonged critical illness, we investigated whether reduced TRH could be the result of feedback inhibition exerted by increased local T3 levels in the hypothalamus. We found increased D2 mRNA and increased thyroid hormone transporter gene expression (MCT10 and OATP1C1) in prolonged critically ill animals. These changes could lead to increased local T3 levels supporting our hypothesis. However, local T4 levels in the hypothalamus were lower in the critically ill than in healthy control animals, whereas local T3 levels were similar.

There was no change at the thyroid hormone receptor level.By in situ hybridization staining we observed an almost complete loss of TRH signal in the PVN of prolonged ill animals. This confirms data from Fliers and colleagues who have clearly shown that TRH is reduced during prolonged critical illness [4].D2 gene expression was markedly increased in the mediobasal hypothalamus Anacetrapib in the prolonged critically ill state as was seen by in situ hybridization staining.