Thyroid hormones and thermogenesis: a microcalorimetric study of overall cell metabolism in lymphocytes from patients...

We used microcalorimetry to measure lymphocyte heat production rate in patients with clinical and laboratory hyperthyroidism (serum TSH decreases, serum FT4 increases, serum FT3 increases), subclinical hyperthyroidism (serum TSH decreases, serum FT1 increases, serum FT3 =), and subclinical hypothyroidism (serum TSH increases, serum FT4 decreases, 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 less than 0.01) and to the free triiodothyronine level (r = 0.51, p less than 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 less than 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.