Growth hormone has mitotic and anti-apoptotic effects which may increase proliferation and transformation of cells when it is expressed aberrantly. This study investigated the effects of resistance training and growth hormone injection on circulating IGF-1, IGFBP-3 levels and IGF-1/IGFBP-3 ratio in male Wistar rats. Thirty-two male Wistar rats were randomly assigned to a control group (C, n = 8), a resistance training group (RT, n = 8), a growth hormone injection group (GI, n = 8) and a resistance training + growth hormone injection group (RG, n = 8). The resistance training protocol comprised of climbing a ladder (5 days/week, 3 sets/5 reps) while carrying a weight suspended from the tail. The growth hormone (2 mg/kg/day, 5 days/week) was injected before an exercise session. Serum IGF-1, IGFBP-3 levels, and IGF-1/IGFBP-3 ratio were measured after 8 weeks. One-way ANOVA analysis was used for comparison of serum IGF-1 and IGFBP-3 levels between groups. Serum IGF-1 levels and IGF-1/IGFBP-3 ratio signifi cantly decreased, but serum IGFBP-3 levels showed no significant change in the RT group compared to the C group. Also, both serum IGF-1 and IGFBP-3 levels and IGF-1/IGFBP-3 ratio in GI and RG groups significantly increased compared to the other groups. In conclusion, resistance training decreases serum IGF-1 levels and/or IGF-1/IGFBP-3 ratio in normal condition. On the other hand, the growth hormone injection with and without the resistance training increases serum IGF-1 levels and IGF-1/IGFBP-3 ratio which could be noted as a condition with a higher risk of neoplasm.
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