INFLUENCE OF EXPERIMENTAL HYPERTHYROIDISM ON SKELETAL MUSCLE METABOLISM IN THE RAT

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Abstract
In this study hind-limb perfusion was used to investigate the influence of thyroid hormones on some metabolic parameters in the skeletal muscle of the rat. Daily injection of 20 μg L-thyroxine (T4) per 100 g b. w. for a week caused a 25 % increase in oxygen consumption. Further enlargement of the T4 dose had little additive effect. In the dose range 20–80 μg T4/100 g b. w., no important changes occurred in lactate production or glucose consumption. Only at the highest T4 dose did the glucose consumption increase significantly. The most profound effect of T4 was on lipolysis. A daily dose of 20 μg T4/100 g b. w. gave a doubling of glycerol production rate, the maximum occurring at a dose of 40 μg T4/100 g b. w Inactivation of the nervous system was without influence on the T4-induced increase in oxygen consumption. However, the T4-induced elevation of lipolysis disappeared after abolition of the nervous activity. This raises the possibility that the T4 effect on lipolysis in skeletal muscle is a potentiation of catecholamine effects. The T4-induced oxygen consumption increase might be dependent not on the lipolytic process but rather on other energy-consuming cell processes.

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