Submitted on January 20, 2006
Accepted on July 5, 2006
The Effect of rhIL-6 Infusion on GH
IGF-I Axis Mediators in Humans
Dan Nemet1, Alon Eliakim1, Frank Zaldivar2, and Dan M Cooper2*
1 Child Health and Sports Center, Meir General Hospital, Sackler School of Medicine, Tel Aviv University, Kfar Saba, Israel; Pediatric Exercise Research Center, University of California, Irvine, Orange, California, United States
2 Pediatric Exercise Research Center, University of California, Irvine, Orange, California, United States
* To whom correspondence should be addressed. E-mail: dcooper{at}uci.edu.
Exercise leads to simultaneous increases in mediators signaling apparently antagonistic responses such as growth factors and inflammatory mediators. The aim of the present study was to demonstrate the physiological effect of IL-6 on circulating components of the growth hormone (GH) - insulin-like growth factor-I (IGF-I) axis. Twelve men (ages 26±2 yrs) were divided into two groups, receiving either albumin or rhIL-6 infusion. IL-6 dose was chosen to reach plasma levels of IL-6 characteristic of prolonged intense exercise (5 µg/h, for 3h, resulting in plasma levels of 100 pg/ml). Blood samples for GH, GH binding protein (GHBP), IGF-I, IGFBP-1,3 and ALS were collected at baseline, 30min, 1h, 2h, 3h, 4h, 5h and 8h after the beginning of the infusion. IL-6 levels increased only in the rhIL-6 infused group (p<0.0005), and returned to baseline after the infusion was stopped. IL-6 infusion led to a significant increase in GH, peaking one hour after the beginning of infusion (p<0.001). A decrease in total IGF-I levels was noted only in the rhIL-6 infused group (p<0.027). An initial decrease in IGFBP-1 levels was noted in both groups (P<0.03). Following this decrease, there was a significant increase in IGFBP-1 levels only in the IL-6 infused participants peaking at 2h after the infusion cessation (P<0.001). IL-6 infusion had no effect on GHBP, IGFBP-3 and ALS levels. rHIL-6 levels similar to the levels found after strenuous exercise induced a typical exercise-associated GH
IGF-I axis response. The results suggest that IL-6 plays a role in the GHIGF-I response to intense exercise.
