Thyroid hormones action, calorigenic

The effect of thyroid hormones on oxidative processes has long been considered to be their most fundamental action in adult mammals. In 1895, Magnus-Levy made the classic observation that respiratory exchange is depressed in hypothyroidism and elevated in hyperthyroidism. Many factors modify the effect of thyroid hormones in the intact animal, such as nutrition, other endocrine secretions, and the general health of the animal (cf. Boothby and Sandiford, 1924 Sundaram el al., 1956 Money, 1956) a consideration of these fa( tors is beyond the scope of this review. It should be noted that the thyroid hormones appear to exert no calorigenic activity in lower vertebrates (cf. Fromm and Reineke, 1956). 

A calorigenic action of thyroid hormones can also be demonstrated in tissues excised from animals with experimentally induced hyperthyroidism. In 1924, Rohrer demonstrated increased oxygen consumption in liver, kidney, and muscle isolated from mice which had been made hyperthyroid with desiccated thyroid. Most subsequent experiments have been performed with tissue sUces excised from other species, especially the rat. Differences in the metabolic responses of various tissues to thyroid stimulation have been ob.served, depending upon the species studied and the thyroid preparations used these differences will be discussed in the subsequent section. In contrast to the response of isolated tissues to thyroid hor-... 

Ismail-Beigi, F. and Edelman, I. S. (1971). The mechanism of calorigenic action of thyroid hormone stimulation of Na+ and K+-activated adenosine triphosphatase activity. J. Gen. Physiol. 57 710-722. 

The natural thyroid hormone, levorotatory thyroxine (LTJ, is primarily responsible for the elevation of the basal metabolic rate (BMR) as reflected in the increase in oxygen consumption. This feature of thyroxine is denoted as the calorigenic effect. Another important property of thyroxine is its influence on the heart. The intrinsic heart-rate was found to be higher in patients with hyperthyroidism and lower than normal in patients with hypoth5U oidism. It has been concluded that the differences in heart-rate between subjects with hyper- and hypothyroidism are mainly due to thyroxine acting directly on the heart and not to its potentiation of the action of catecholamines [174]. 

Localization of the calorigenic action of thyroxine in the hver may be achieved to a certain degree by enhancement of the transfer of the thyroid hormone from... 

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