Thermogenesis, thyroid hormones

Thyroid hormones are intimately involved in regulating the basal metabolic rate. Liver tissue of animals given excess thyroxine shows an increased rate of 02 consumption and increased heat output (thermogenesis), but the ATP concentration in the tissue is normal. Different explanations have been offered for the thermogenic effect of thyroxine. One is that excess thryroxine causes uncoupling of oxidative phosphorylation in mitochondria. How could such an effect account for the observations Another explanation suggests that the thermogenesis is due to an increased rate of ATP utilization by the thyroxine-stimulated tissue. Is this a reasonable explanation Why ... 

Silvestri E, Schiavo L, Lombardi A, Goglia F. Thyroid hormones as molecular determinants of thermogenesis. Acta Physiol Scand. 2005 184 265-283. 

Thermogenesis. T4 and T, increase the basal metabolic rate and subsequent heat production from the body, which are important in maintaining adequate body temperature during exposure to cold environments. Increased thermogenesis is achieved by thyroid hormone stimulation of cellular metabolism in... 

Dauncey, M.J. (1990). Thyroid hormones and thermogenesis. Proc. Nutr. Soc. 49,203-215. 

In the neonate, neural NE promotes nonshivering thermogenesis, i.e., heat production via stimulation of lipolysis and fatty acid oxidation in brown adipose tissue ( 63) with the support of thyroid hormone. Brown adipose tissue contains a high density of mitochondria with an uncoupling protein that allows the cells to oxidize fatty acids and generate heat as a major product NE released at nerve endings stimulates cAMP-mediated lipolysis in these cells and promotes thermogenesis by this y83-mechanism (Chapter 14). 

IDL) to LDL, and probably also by maintaining lipoprotein lipase activity which promotes triglyceride clearance. In liver, kidney, skeletal muscle, cardiac muscle, and adipose tissue, thyroid hormone stimulates Na", K+-ATPase gene expression and promotes thermogenesis. 

Van der Linden, C.G., Muller, A. and Van Hardeveld, C. (2001) Mechanism of thyroid-hormone regulated expression of the SERCA genes in skeletal muscle implications for thermogenesis. Bioscience Reports, 21, 139—154. 

Because most of the energy produced by cellular respiration eventually appears as heat, an increase in cellular respiration necessarily leads to an increase in heat production (i.e., to a thermogenic or calorigenic effect). Thus, to the degree that thyroid hormones control BMR, they also control thermogenesis (17). 

Muller MJ, Seitz HJ. Thyroid hormone action on intermediary metabolism. Part I respiration, thermogenesis, and carbohydrate metabolism. Klin Wochenschr 1984 62 11-18. 

Beta-adrenoceptor antagonists are used in the treatment of hyperthyroidism to alleviate symptoms but are not considered to influence thyroid hormone production nor the effect of the hormone on cell function. A study of the effect of beta-blockers on lymphocyte metabolism was done with the purpose to clarify their mechanism of action in hyperthyroidism [68]. When hyperthyroid subjects were treated with beta-blockers, lymphocyte heat production was found to be within normal limits, thus showing that beta-blockers prevent the expected increased of cell metabolism under stimulation of thyroid hormone. These results seem to indicate that increased thermogenesis in hyperthyroidism is mediated via adrenergic receptors, rather than via nuclear thyroid hormone receptors. 

In a group of haemodialysis patients, muscle thermogenesis was evaluated by measurement of heat production in skeletal muscle samples [112]. Biopsies were taken from the vastus lateralis muscle by needle technique, using the same amount of muscle for each patient, about 45 mg. Microcalorimetric measurements were made in a perfusion calorimeter of the thermopile heat conduction type, as previously described. Blood samples for measurement of thyroid hormone concentration were collected the morning before dialysis after the patients had been fasting for 12 h. About 40% of the group of haemodialysis patient were found to have decreased muscle heat production... 

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