High-affinity growth hormone binding protein and acute heavy resistance exercise
Rubin, MR and Kraemer, WJ and Maresh, CM and Volek, JS and Ratamess, NA and VanHeest, JL and Silvestre, R and French, DN and Sharman, MJ and Judelson, DA and Gomez, AL and Vescovi, JD and Hymer, WC, High-affinity growth hormone binding protein and acute heavy resistance exercise, Medicine and Science in Sports and Exercise, 2005 Mar, (37(3)) pp. 395-403. ISSN 0195-9131 (2005) [Refereed Article]
PURPOSE: The purpose of this investigation was to examine the influence of resistance training on circulating concentrations of growth hormone binding protein (GHBP) in response to acute heavy resistance exercise.
METHODS: Using a cross-sectional experimental design, a group of resistance-trained men (RT, N=9, 7.9+/-1.3 yr resistance training experience) and a group of untrained men (UT, N=10) performed an acute heavy resistance exercise protocol (AHREP) consisting of 6 sets of 10 repetition maximum parallel squats. Blood samples were obtained 72 h before exercise, immediately before exercise, and 0, 15, 30, 45, and 60 min after exercise.
RESULTS: Significant increases (P<0.05) in GHBP, immunoreactive growth hormone (iGH), and IGF-1 were observed in both subject groups after AHREP. There were no differences (P>0.05) between groups in GHBP at rest or after AHREP. However, RT exhibited a significantly greater iGH response to AHREP than UT subjects, and significantly higher IGF-1 values at rest and after exercise. Significant positive correlations were found between GHBP and BMI, body fat, and leptin in both groups. A significant positive correlation also was observed between resting leptin and GHBP values in UT but not RT subjects.
CONCLUSIONS: In summary, these data indicate that resistance training does not increase blood GHBP. Nevertheless, the increases observed with IGF-1 concentrations in the resistance-trained subjects do suggest an apparent adaptation with the regulation of this hormone. If there was in fact an increase in GH sensitivity and GH receptor expression at the liver that was not detected by blood GHBP in this study, it may be possible that factors contributing to the circulating concentration of GHBP other than hepatocytes (e.g., leptin and adipocytes) may serve to mask training-induced increases in circulating GHBP of a hepatic origin, thus masking any detectable increase in GH receptor expression.