Acute effect of physical exercise on serum insulin-like growth factor-binding protein 2 and 3 in healthy men: Role of exercise-linked growth hormone secretion

The purpose of this study was to delineate the role of GH on serum IGF-1, IGFBP-2 and -3 responses to exercise. Hormones were evaluated in six trained male subjects before (- 30, - 15, 0), during (+ 15) and after (+ 30, + 45, + 60, + 90 min) a thirty-minutes treadmill exercise (60% (V) over dot O(2)max), both after a single administration of a somatostatin analog (i.e., octreotide, 0.1 mg sc) and after saline. The same evaluations were performed without exercise with similar treatments. The results showed that: 1) octreotide significantly inhibited the GH response to exercise, 2) exercise increased IGFBP-3 concentration (+37.4% at +90, p<0.05), whereas no modification of IGFBP-2 and of IGF-1/IGFBP-2 and IGFBP-3/IGFBP-2 ratios were observed, 3) octreotide amplified the IGFBP-3 increase after exercise (p<0.01 vs. exercise, from + 30 to + 60, or octreotide alone) and, without exercise, slightly increased IGFBP-3 (+15% at +75, p<0.05) and decreased IGF-1 (-14.8% at +75, p<0.01). We concluded that GH has a reduced role, as a stimulating factor, in the serum acute IGFBPS increase after exercise and that octreotide is probably able to directly amplify this response. Unfortunately, we can only speculate on the physiological pathways involved.