Phytoecdysteroids increase protein synthesis in skeletal muscle cells.

Phytoecdysteroids, which are structurally similar or identical to insect molting hormones, produce a range of effects in mammals, including increasing growth and physical performance. To study the mechanism of action of phytoecdysteroids in mammalian tissue, an in vitro cellular assay of protein synthesis was developed. In C2C12 murine myotubes and human primary myotubes, phytoecdysteroids increased protein synthesis by up to 20%. In vivo, ecdysteroids increased rat grip strength. Ecdysteroid-containing plant extracts produced similar results. The effect was inhibited by a phosphoinositide kinase-3 inhibitor, which suggests a PI3K-mediated mechanism.