Hormonal regulation of muscle fibres characteristics : a review

Abstract

During postnatal development, the growth of skeletal muscle and the diversification of muscle fibre types are regulated by genetic, nutritional and endocrine factors. Herein, the crucial role played by several hormones will be reviewed with regard to their influence on fibre distribution and on myosin expression. Somatotropic hormones (GH and IGF-I) do not affect fibre composition but appear to regulate myosin isoform expression. Thyroid hormone increases the proportion of fast compared to slow fibres and the expression of fast myosin. Insulin influences fibre properties since a decrease in the fast IIB fibre percentage and a decrease in fast native isomyosins characterise insulinodependent diabete. Beta-adrenergic agonists increase the proportion of IIB fibres. The extend to which they modify contractile properties has still to be characterised. Sex steroids differentially affect muscle fibres. Anabolic androgens decrease the proportion of IIB fibres and the expression of IIb myosin heavy chain whereas estrogens do not influence fibre types. On the opposite, glucocorticoids induce muscle fibres atrophy and decrease the proportion of IIB fibres. Their impact on myosin expression has received little attention. Increasing knowledge of how these hormones affect muscle fibres properties could have relievant applications in meat-producing farm animals.