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-I, 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˙O₂max), 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-I/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-I (- 14.8 % at + 75, p < 0.01).

We concluded that GH has a reduced role, as a stimulating factor, in the serum acute IGFBP-3 increase after exercise and that octreotide is probably able to directly amplify this response. Unfortunately, we can only speculate on the physiological pathways involved.

GH, IGF-I, IGFBP-2, IGFBP-3, octreotide, physical exercise.

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