Thyroid hormones and thermogenesis: A microcalorimetric study of overall cell metabolism in lymphocytes from patients with different degrees of thyroid dysfunction

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Abstract
We used microcalorimetry to measure lymphocyte heat production rate in patients with clinical and laboratory hyperthyroidism (serum TSH .dwnarw., serum FT4.uparw., serum FT3.uparw.), subclinical hyperthyroidism (serum TSH .dwnarw., serum FT4.uparw., serum FT3=), and subclinical hypothyroidism (serum TSH .uparw., serum FT4.dwnarw., serum FT3=) compared with healthy controls (N = 13). The lymphocyte heat production rate was significantly correlated to the free thyroxine level (r=0.53, p<0.01) and to the free triiodothyronine level (r=0.51, p<0.01) when calculated from pooled data for the three patients groups. The hyperthyroid patients (N=8) had a significantly increased lymphocyte heat production rate, 3.43.+-.0.25 pW/cell, as compared with 2.31.+-.0.12 pW/cell in the control group (p<0.001).The groups with subclinical hyperthyroidism (N=7) and subclinical hypothyroidism (N=9) had lymphocyte heat production rates of 2.14.+-.0.11 and 2.56.+-.0.15 pW/cell, respectively, not significantly different from that in the controls. Consistently, there was no significant difference between patients with subclinical hyperthyroidism (N=5) and controls (N=5) with regard to lymphocyte energy production as calculated from separately measured oxygen consumption rates in vitro, 1.36.+-.0.20 and 1.56.+-.0.12 pW/cell, respectively. Thus microcalorimetry seems to be suitable for studying the influence of thyroid hormones on cellular metabolism. Subclinical thyroid dysfunction does not seem to alter the overall rate of lymphocyte metabolism.