Hormonal and nutritional determinants of catch-up growth in hamsters

Exercise accelerates somatic and skeletal growth in mature nondeprived hamsters and induces catch-up growth when food restriction during exercise is followed by ad libitum realimentation. The hypothesis that nutrient availability controls the rate of growth through changes in anabolic hormone release was tested through measurements of serum growth hormone (GH) and insulin concentrations at the same time of day in exercising and sedentary hamsters subjected to acute fasts, chronic food restriction, and to acute and prolonged realimentation. Concentrations of GH and insulin increased in ad libitum-fed exercising hamsters, but these increases were abolished by 12 and 4 h of fast, and restored by 4 and 2 h of refeeding, respectively. Four h of refeeding restored exercise-induced increases in serum GH, but not in serum insulin concentration in chronically food-restricted hamsters. During catch-up growth, the growth rate was double that of ad libitum fed exercising hamsters, but the increases in serum GH concentration in the two situations were similar. I conclude that increases in serum GH rather than in serum insulin concentration are the most probable determinant of exercise-induced growth and catch-up growth because they are relatively refractory to short-term nutritional perturbations.