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 facilitate d the study of the metabolic effects of nutrients and hormones, particularl y in children. This brief review examines recent work on the effects of gro wth hormone (GH), insulin-like growth factor I (IGF-I), testosterone and oe strogen on rates of protein synthesis and degradation and lipolysis, as wel l as on body composition and bone calcium fluxes in young children and adul ts. GH acts indirectly on whole body protein pools via IGF-I, but GH appear s to act directly on lipolysis. Testosterone stimulates protein synthesis i ndependently 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 un derscoring the importance of both groups of hormones in bone calcium metabo lism. Further understanding of the physiological role of these hormones dur ing the critical years of adolescence will give us better tools with which to treat disorders of puberty and growth.