Insulin, Glucose, and Glucagon are Potential Modulators of Thyroid Hormone Action Through Brown Adipose Tissue 5′-Deiodinase in Rats
Brown adipose tissue (BAT) contains Type II iodothyronine 5′deiodinase (5′D) (1). At variance with other tissues containing this enzyme, BAT 5′D is markedly stimulated by the sympathetic nervous system (2). This stimulation is physiologically relevant since it results in several-fold increments in locally-produced BAT T3 and generation of circulating T3 (3). These results, previously reported by us, suggest that BAT may become an important source of circulating T3 and, further, that T3 may have an important physiological role in the function of this tissue. Probably the main function of BAT is to generate heat through the oxidation of fatty acids uncoupled from ATP generation, which in turn is important for body temperature regulation and for dissipation of excess calories in the overfed state. Conversely, fasting and carbohydrate deprivation depress thermogenesis and the metabolic activity of BAT. We observed earlier that an adequate glucose supply was necessary for the elevation of BAT 5′D to occur following hypophysectomy. Altogether, these observations prompted us to examine the influence of insulin, glucagon, carbohydrate feeding, and fasting on BAT 5′D and its responses to various stimuli.
KeywordsSympathetic Nervous System Brown Adipose Tissue Howard Hughes Medical Institute Thyroid Hormone Action Excess Calorie
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