EFFECT OF MARATHON RUN ON SERUM IGF-I AND IGF-BINDING PROTEIN-1 AND PROTEIN-3 LEVELS

Acute physical exercise increases growth hormone (GH) secretion, and G H regulates the expression of insulin-like growth factor I (IGF-I) and IGF-binding protein (IGFBP) 3. IGFBP-1 is a local modulator of IGF ac tivity with rapid dynamic regulation that is downregulated by insulin. The IGF system mediates the metabolic actions of GH, and possibly it regulates glucose metabolism. We hypothesize that strenuous exercise c auses changes in the IGF system. We studied the effects of the maratho n run on the circulating levels of IGF-I, IGFBP-1, IGFBP-3, and insuli n in 23 participants. Immediately after the run, the most striking cha nge was an 11.6-fold median increase in serum IGFBP-1 level (from 63.7 +/- 50.5 to 736 +/- 408 mu g/l; P < 0.001). Because the insulin level remained unchanged, the elevation of serum IGFBP-1 level cannot be ex plained by changes in insulin. One day after the run, the IGFBP-1 leve l had returned to baseline. The physiological role of this increment c ould be the inhibition of hypoglycemic effects of IGF-I and/or regulat ion of glucose availability to the muscles. The changes in IGF-I and I GFBP-5 levels were less dramatic: the IGF-I and IGFBP-5 levels were lo wer 1 and 3 days after the run. This report provides an important basi s for authentic effects of strenuous exercise on the IGF-system.