Exercise stimulates hepatic insulin-like growth factor binding protein-1 (IGFBP-1) mRNA expression in rats

IGFBP-1 and IGFBP-2 expression was determined in serum and tissues of exercised, fasting rats to examine the role of these binding proteins during recovery from exercise. Male Sprague-Dawley rats (-200 g) were run on a treadmill at 26 m/min (1.5% grade) for 90 minutes. Food was removed from all animals 4 hr before exercise. Exercised animals (EX) and non-exercised controls (C) were killed 15 min, l, 4, 8, and 12 hrs postexercise, and serum, liver and muscle were obtained. Serum IGF-I, insulin, and growth hormone (GH) were determined by RIA. Serum IGFBP-1 and BP-2 were estimated by densitometric scanning of the 29-31 kDa band on SDS-PAGE Western ligand blots. Hepatic IGFBP-1 and BP2 mRNA expression was determined by Northern analysis. Serum GH was significantly higher in EX at 15 min, l, 4 and 8 hrs post-exercise, but serum IGF-I and insulin in EX were either slightly depressed or not different from C at all time points. The 29-31 kDa band was 3-fold and 2fold greater in EX than C at 15 min and 1 hr, respectively; whereas by 12 hr, the 29-31 kDa band was increased 5-fold in both EX and C. Northern analysis revealed increased hepatic IGFBP-1 mRNA expression in EX at 15 min and 1 hr, but not in IGFBP-2. However, hepatic IGFBP-2 mRNA expression was increased at 4, 8 and 12 hr in both groups. These results suggest that recovery from exercise is associated with an acute, short-term increase in IGFBP-1 mRNA expression independent from fasting. In contrast, IGFBP-2 mRNA was stimulated after 9 hrs of food deprivation.