The effects of growth hormone on body composition

The action of growth hormone (GH) on longitudinal bone growth is well known and easily recognized. GH also has profound effects on body composition. Generally, GH increases the amount of body cell mass and extracellular water and decreases body fat. The lipolytic effect of GH was demonstrated in the 1930s when it was shown that pituitary extracts reduced body fat in rats. Recently, GH treatment has been shown to promote a redistribution of adipose tissue from the abdominal (android) to a more peripheral (gynoid) distribution. The reverse change has been demonstrated in patients with acromegaly after successful treatment. The anabolic action of GH was first demonstrated when nitrogen retention was observed after GH administration. GH seems to stimulate cell division and increase the amount of DNA in the muscle. In patients with acromegaly the overweight is partly explained by a significant increase in body cell mass and muscle volume, compared to matched controls, demonstrated by several independent methods of determining body composition. In GH-deficient patients, however, the overweight is due to an increase in adipose tissue mass and the body cell mass seems only decreased in subjects below the age of 55. The anabolic action of GH is accompanied by sodium and fluid retention, due to increased sodium pump activity. In acromegalic subjects extracellular water has been shown to be increased by up to 25%. However, in GH-deficient adults the extracellular fluid volume is markedly decreased by approximately 15%. Replacement therapy with recombinant human GH in patients with GH deficiency restores the extracellular fluid volume by an initial rapid expansion of the fluid volume, followed by a slight decrease towards a new steady-state level. GH has profound effects on body composition. Although body composition is determined by many factors including age and physical activity, changes in body composition can be helpful parameters in following the effect of GH in various body compartments.