Objectives. We investigated the effect of short- and long-term swimming exercise, with or without insulin-like growth factor (IGF)-I administration, on the expression of myocardial IGFs and contractile proteins. Methods. Sprague-Dawley male rats (n = 36) were subjected to swimming exercise for 2 or 6 weeks. IGF-I (0.5 mg/rat) was administered continuously for 1 week, using alzet osmotic pumps. Control groups remained sedentary. IGF-I, IGF-I receptor (IGF-IR), IGF-II, skeletal α-actin (sk-actin), and β myosin heavy chain (βMHC) mRNAs were measured using Northern blot analysis and RT-PCR. Results. A significant 2-fold increase in myocardial IGF-I mRNA was found after 2 and 6weeks of swimming in both IGF-I treated and untreated rats (p < 0.001). IGF-IR mRNA was significantly (p < 0.05) increased after 6 weeks of training only in the IGF-I treated animals. IGF-II mRNA remained unchanged at all time points. While βMHC mRNA was significantly decreased (p = 0.003) at 2 and 6 weeks, sk-actin mRNA remained unchanged. Conclusions. Short- and long-term swimming exercise training increase myocardial expression of IGF-I mRNA. Exogenous administration of IGF-I, during the first week of the exercise session, did not produce any effect on myocardial IGF-I but was associated with increased IGF-IR signal after the long-term exercise training. These data suggest a relationship between IGF-I expression and cardiac adaptation to exercise training.
- IGF-I receptors
- Myocardial contractile proteins