Evidence that the Thyroid State Influences Ca⁺⁺-Mediated Metabolic Processes in Perfused Skeletal Muscle

Summary

The effects of ouabain- and K⁺-induced depolarization on muscle oxygen consumption, lactate release, and glucose consumption in hypothyroid and euthyroid rats were studied in the presence and absence of dantrolene sodium. In addition, K⁺ release was measured in the experiments with ouabain.

In hypothyroid rats, ouabain addition (0.25 mM) led to an oxygen consumption decrease of 17%, whereas in the controls this consumption increased by 53%. Stimulation of lactate release by ouabain was 4 times higher in euthyroid than in hypothyroid rats. Glucose consumption was slightly but significantly elevated by ouabain in both groups. Dantrolene sodium abolished the ouabain-induced stimulation of oxygen consumption and lactate release. K⁺ release was 45% lower in hypothyroid rats than in the controls after ouabain addition. No effect of dantrolene sodium on K⁺ release was observed in either group.

Elevation of the K⁺ concentration to 20 mM stimulated oxygen consumption and lactate release in both groups, but to a lower degree in the hypothyroid group. The K⁺-induced increase in oxygen consumption was abolished and the lactate-release was strongly diminished by dantrolene sodium in both groups.

These results provide evidence that the thyroid state alters the response to Ca⁺⁺-mediated metabolic processes in skeletal muscle.

Key-Words:

Skeletal Muscle - Ouabain - K+-induced Depolarization - Dantrolene Sodium - Thyroid State