Effect of Exercise Training on Red Blood Cell (RBC) Insulin-like Growth Factor-I (IGF-I) Receptor Binding in Adolescent Males. † 399

Abstract

Exercise training likely leads to tissue anabolism (e.g., muscle hypertrophy) by acting through the growth hormone (GH)-IGF-I axis, but the role of tissue IGF-I receptors in this process is not known. RBC IGF-I receptor binding (most likely reflecting erythroid precursors) has been characterized and is known to be affected by circulating IGF-I levels. Thus, we hypothesized that training would lead to alterations in IGF-I binding in RBCs. 38 adolescent males (16±0.7 y.o.) were randomized to a control(n=18) and endurance type training intervention lasting 5 weeks. RBC IGF-I binding was measured by standard techniques in which native 125I-IGF-I was displaced with unlabelled IGF-I. Iterative curve fitting algorithms were used to calculate the binding affinity constant (Kaff), number of binding sites (R), and nonspecific binding. Training led to (*p<0.05) increases in Kaff, KaffR (an index of overall binding capacity), and nonspecific (NS) binding. These results suggest a possible upregulation of IGF-I binding, and may be related to training induced changes in circulating and/or local IGF-I levels. The unexpected increase in nonspecific binding may reflect a role of RBC associated binding proteins, rather than changes in IGF-I receptors themselves. Figure