Effect of brief exercise on circulating insulin-like growth factor I

An acute insulin-like growth factor I (IGF-I) response to 10 min of above-lactate threshold cycle ergometer exercise was studied in 10 subjects (age 22–35 yr). Each subject exercised on three separate mornings after ingesting one of two isocaloric isovolemic liquid meals high in either fat or glucose or an isovolemic noncaloric placebo. The high-fat meal attenuated the growth hormone (GH) response (Cappon et al., J. Clin. Endocrinol. Metab. 76: 1418–1422, 1993). In contrast, IGF-I increased equally for all protocols [e.g., after the placebo meal IGF-I increased from 21,716 (SE) ng/ml preexercise to 25,316 ng/ml at 10 min of exercise; P < 0.05]. IGF-I peaked by the 10th min of exercise, like GH, and remained significantly elevated for only 20 min of recovery. We tested for possible GH-dependent mechanisms in which circulating IGF-I would increase 12-24 h after exercise. Ten subjects (age 23–32 yr) performed 10 min of above-lactate threshold exercise at 9, 10, and 11 A.M. GH was elevated after the first exercise bout (peak GH 6.05 +/- 1.45 ng/ml; P < 0.001) but was significantly reduced for the second and third bouts (peak GH 2.52 +/- 0.76 and 1.50 +/- 0.40 ng/ml, respectively). No increase in IGF-I was observed by 8 A.M. on the following day. Heavy ergometer exercise led to brief and small increases in circulating IGF-I that were independent of circulating GH.(ABSTRACT TRUNCATED AT 250 WORDS)