Submitted to: American Journal of Physiology Regulatory Integrative and Comparative Physiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/9/2011
Publication Date: 6/1/2011
Citation: Scofield, D.E., Mcclung, H.L., Mcclung, J.P., Kraemer, W., Rarick, K., Pierce, J.R., Cloutier, G., Fielding, R.A., Matheny, R.W., Young, A. 2011. A novel, non-invasive transdermal fluid sampling methodology: IGF-I measurement following exercise. American Journal of Physiology Regulatory Integrative and Comparative Physiology. 300(6):R1326-1332. Interpretive Summary: In this study we examined whether we could monitor changes in a specific hormone in the blood, insulin-like growth factor I (IGF-1), by measuring its concentration in fluid that collects on the skin (transdermal fluid). Young health subjects either performed cycling exercise for one hour or performed ten set of calisthenics (10 repetitions). We observed that during and after cycling there were no changes in the blood or transdermal concentrations of IGF-1. However, following the calisthenics the blood concentration of IGF-1 did not increase, but the transdermal concentration obtained over the thigh muscle did increase. This study demonstrates the utility of a non-invasive method for monitoring IGF-I in transdermal fluid when sampled near the exercising muscle.
Technical Abstract: This study tested the hypothesis that transdermal fluid (TDF) provides a more sensitive and accurate measure of exercise-induced increases in insulin-like growth factor-I (IGF-I) than serum, and that these increases are detectable proximal, but not distal, to the exercising muscle. A novel, noninvasive methodology was used to collect TDF, followed by sampling of total IGF-I (tIGF-I) and free IGF-I (fIGF-I) in TDF and serum following an acute bout of exercise. Experiment 1: eight men (23 +/- 3 yrs, 79 +/- 7 kg) underwent two conditions (resting and 60 min of cycling exercise at 60% Vo(2)(peak)) in which serum and forearm TDF were collected for comparison. There were no significant changes in tIGF-I or fIGF-I in TDF obtained from the forearm or from serum following exercise (P > 0.05); however, the proportion of fIGF-I to tIGF-I in TDF was approximately fourfold greater than that of serum (P = 0.05). These data suggest that changes in TDF IGF-I are not evident when TDF is sampled distal from the working tissue. To determine whether exercise-induced increases in local IGF-I could be detected when TDF was sampled directly over the active muscle group, we performed a second experiment. Experiment 2: fourteen subjects (22 +/- 4 yr, 68 +/- 11 kg) underwent an acute plyometric exercise condition consisting of 10 sets of 10 plyometric jumps with 2-min rest between sets. We observed a significant increase in TDF tIGF-I following exercise (P = 0.05) but no change in serum tIGF-I (P > 0.05). Overall, these data suggest that TDF may provide a noninvasive means of monitoring acute exercise-induced changes in local IGF-I when sampled in proximity to exercising muscles. Moreover, our finding that the proportion of free to tIGF-I was greater in TDF than in serum suggests that changes in local IGF-I may be captured more readily using this system.