Time course changes in IGFBP-1 after treadmill exercise and postexercise food intake in rats

Prolonged exercise increases circulating insulin-like growth factor binding protein-1 (IGFBP-1) in humans and animals, but its physiological significa nce is unknown. This study examined 1) time-course changes in plasma IGFBP- 1 and hepatic IGFBP-1 mRNA expression after exercise, 2) changes in IGFBP-1 in relation to plasma glucose, insulin, and IGF-I, and 3) the impact of fe eding a postexercise meal on the IGFBP-1 response. Food-deprived male rats were vigorously run on a treadmill and compared with nonexercised controls at 15 min and 1, 4, 8, and 12 h after exercise. Circulating insulin concent rations in exercised rats were lower than in controls at 15 min and 1 h, wh ereas plasma glucose and IGF-I remained unaffected. Circulating and hepatic expression of IGFBP-1 was markedly increased above that of controls at 15 min, 1 h, and 12 h. In a separate experiment, one-half of the exercised ani mals received a nutritionally complete meal immediately after the experimen tal run. The meal elevated plasma insulin and glucose concentrations at 15 min and 1 h. Despite this change in nutritional status, serum IGFBP-1 conce ntrations and hepatic IGFBP-1 abundance remained elevated at 15 min and 1 h . These results demonstrate that the IGFBP-1 response to a single bout of t readmill exercise is short in duration and independent of insulin, glucose, and amino acid availability.