Thyroid hormone deficiency and muscle metabolism during light and heavy exercise in dogs.

Muscle glycogen, glycolytic intermediate and high energy phosphate contents were compared in 5 intact-control (C) and thyroidectomized (THY) dogs after 30 min treadmill exercise of low (40W) and high (70W) intensities. Although after the exercise of relatively low intensity the rate of glycogenolysis and muscle lactate accumulation in THY dogs exceeded those in controls, the diminished oxidative capacity in the former was inadequately compensated, resulting in lowering of APT and CrP contents. At the higher work load the latter effects were more pronounced while the rate of glycogenolysis was similar or even lower than in controls. Inadequate fuel utilization may be considered as a factor limiting ability for heavy exercise in hypothyroidism.