Increased serum growth hormone and somatic growth in exercising adult hamsters

In freely feeding adult hamsters, voluntary exercise induces accelerated somatic growth and increased food consumption that last through several days of retirement. We examined the effects of exercise on serum concentrations of growth hormone (GH) and insulin during ad libitum or restricted intake of food. Serum insulin and GH concentrations were measured by radioimmunoassays in exercising, retired, or sedentary hamsters during ad libitum or restricted intake of food. Linear growth was delayed in food-restricted, exercising hamsters until they were retired and unlimited food consumption was allowed. Serum GH concentrations were increased during exercise and after retirement; serum insulin concentrations were increased only after retirement during both dietary regimes. In food-restricted hamsters, endocrine changes were noted after 4 h of feeding but not after a 14-h fast. We conclude that 1) in adult hamsters voluntary exercise leads to increased secretion of GH even when ingested nutrients are insufficient to support increased growth, and 2) increased secretion of insulin is not related directly to exercise.