Several methods were used to detect changes in thyroid activity and in degradation of thyroxine (T4) in exercising and sedentary control rats. Rats were run in a motor-driven exercise wheel over a three-week period at progressively increasing work loads and then were run 1.5-2 hours per day for 10-14 days before sacrifice. Disappearance of injected T4-125I from plasma was considerably enhanced by exercise. As determined by isotopic equilibration and paper chromatographic methods, T4 concentration was depressed in plasma and elevated in liver of exercised rats. No significant changes in T4 concentration were observed in heart, kidney, or gastrocnemius muscle. Thyroidal iodotyrosine levels were elevated immediately following but not 24 hours after exercise. Serum free T4 was higher in exercised rats. In vitro deiodinating activity in liver, muscle or kidney homogenates was not affected by exercise. The elevated T4 degradation rate accompanying exercise is thus likely due to the elevated free T4. The liver is apparently the tissue site responsible for the increased T4 uptake and degradation.
College and Department
Plant and Wildlife Sciences
BYU ScholarsArchive Citation
Winder, William W., "Effect of exercise on tissue concentrations of thyroid hormones and on thyroxine degradation rate in the rat" (1971). Theses and Dissertations. 7920.
Thyroid hormones; Thyroxine; Exercise; Rats