Growth hormone, insulin-like growth factor I and sex hormones: effects on protein and calcium metabolism

The availability of non‐invasive tracer technologies has greatly facilitated the study of the meta‐bolic effects of nutrients and hormones, particularly in children. This brief review examines recent work on the effects of growth hormone (GH), insulin‐like growth factor I (IGF‐I), testosterone and oestrogen on rates of protein synthesis and degradation and lipolysis, as well as on body composition and bone calcium fluxes in young children and adults. GH acts indirectly on whole body protein pools via IGF‐1, but GH appears to act directly on lipolysis. Testosterone stimulates protein synthesis independently of changes in GH concentrations and acts synergistically with GH to enhance whole body metabolism. Oestrogens and androgens both modulate calcium fluxes, enhancing calcium absorption and retention, and thereby underscoring the importance of both groups of hormones in bone calcium metabolism. Further understanding of the physiological role of these hormones during the critical years of adolescence will give us better tools with which to treat disorders of puberty and growth.