Effects of thyroid hormones on skeletal muscle bioenergetics. In vivo phosphorus-31 magnetic resonance spectroscopy study of humans and rats.

Abstract

The pathophysiology of the myopathy in dysthyroid states is poorly understood. We therefore tested the effects of thyroid hormones on muscle bioenergetics in humans and rats, using in vivo 31P NMR. Two hypothyroid patients had: low phosphocreatine to inorganic phosphate ratio (PCr/Pi) at rest, increased PCr depletion during exercise and delayed postexercise recovery of PCr/Pi. Eight thyroidectomized rats did not show abnormalities at rest, but muscle work induced by nerve stimulation resulted in a significantly (P < 0.0001) lower PCr/ Pi (3545% of control) at each of the three stimulation frequencies tested (0.25, 0.5, and 1.0 Hz). Recovery rate was markedly slowed to one-third of normal values. Thyroxine therapy reversed these abnormalities in both human and rat muscle. Five patients and six rats with hyperthyroidism did not differ from normal controls during rest and exercise but had an unusually rapid recovery after exercise. The bioenergetic abnormalities in hypothyroid muscle suggest the existence of a hormone-dependent, reversible mitochondrial impairment in this disorder. The exercise intolerance and fatigue experienced in hypothyroid muscle may be due to such a bioenergetic impairment. The changes in energy metabolism in hyperthyroid muscle probably do not cause the muscular disease in this disorder.

The effects of hypothyroidism on strength–duration properties of peripheral nerve

“…Proposed mechanisms of this include reduction of fatty acid and carbohydrate metabolism leading to diminished production of ATP [10,11]. Deposits of mucopolysaccharide in peripheral nerves and metabolic disorders of Schwann cells may contribute to peripheral nerve compression and dysfunction in hypothyroid patients [12].…”

Effect of fasting, hypocaloric feeding, and refeeding on the energetics of stimulated rat muscle as assessed by nuclear magnetic resonance spectroscopy.

“…Another possible cause for the observed changes may be the altered thyroid function seen in malnutrition. Malnutrition results in a decrease in T3 and an increase in the less active reverse T3 (26), and it has been shown that the ratio is lower and is restored more slowly postexercise in hypothyroid patients (27).…”

Bio-energetic impairment in human calf muscle in thyroid disorders: a 31P MRS study

“…Therefore, clinically significant changes in skeletal mass and function occur in hypo as well as hyperthyroidism. Mitochondrial metabolism particularly oxidative phosphorylation is said to be altered in both hypothyroid and thyrotoxic state [3][4][5]. However, muscle impairment along with energy metabolism improves dramatically after correction of thyroid dysfunction [5,6].…”