Influence of physical activity on plasma insulin-like growth factor-1 and insulin-like growth factor binding proteins in healthy older women.

It was examined whether physical activity could alter the bioavailability of insulin-like growth factor-1 (IGF-1) which is dependent upon plasma IGF-1 and insulin-like growth factor binding protein (IGFBPs) levels. The potential role that growth hormone (GH) and insulin play in this process was also examined. Seven healthy 62-69-year-old women performed four bouts of physical activity on separate occasions at either a low (L; heart rate = 100 bpm) or moderate intensity (M; heart rate = 120 bpm) for either 25 (S) or 50 (L) min (LS, low intensity/short duration; LL, low intensity/long duration; MS, moderate intensity/short duration; ML, moderate intensity/long duration). GH levels were elevated immediately following the physical activity from 1.3 to 2.6-fold (P < 0.05) whereas IGF-1 levels were not affected by any activity condition. Plasma insulin levels decreased about 35% under all activity conditions (P < 0.05). Plasma levels of IGFBP-1 (BP-1) were decreased immediately following the ML (-47%; P < 0.05) and the LL (-21%) activity bouts and remained lower than initial values 1 h after these activity bouts (-25 and 34%, respectively, P < 0.05). The ML exercise bout resulted in significant (P < 0.05) increases in IGFBP-2 (BP-2) and IGFBP-3 (BP-3) immediately following activity (+31, and +30%, respectively) and these binding proteins remained elevated following the activity (+28, and +48%, respectively). No relationship was found between any changes in plasma GH or insulin, and changes in plasma IGFBPs. Thus, moderate intensity physical activity of long duration may modulate the bioavailability of IGF-1 in the elderly via alterations in BP-1, -2 and -3. However, changes in circulating levels of GH, insulin or IGF-1 do not appear to be regulating IGF-1 bioavailability in response to physical activity.