Cardiovascular and metabolic effects of insulin-like growth factor I at rest and during exercise in humans

To determine whether insulin-like growth factor I (IGF-I) has systemic cardiovascular effects in humans, 60 mu g/kg IGF-I or saline were injected sc in a cross-over, randomized, double blind fashion into eight healthy male volunteers. Cardiac function and performance were evaluated by echocardiography and exercise test. In parallel, the metabolic effects of IGF-I during exercise were investigated. IGF-I improved cardiac performance with a significant increase in stroke volume and cardiac output by 14% and 18% (P < 0.03 and P < 0.04), respectively. Ejection fraction increased by 9% after IGF-I treatment (P < 0.05). Heart rate was not significantly increased at rest or during exercise. Systolic blood pressure was slightly increased by IGF-I, whereas diastolic blood pressure was slightly decreased, resulting in a continuous increase in the blood pressure amplitude at rest and during exercise, but without reaching statistical significance. Maximal exercise duration and peak oxygen consumption were not changed. Exercise was uneventful, without pathological changes on electrocardiogram records. Glucose levels were unchanged, whereas insulin and C peptide levels were decreased by IGF-I at rest. During exercise, insulin levels were further decreased, and the insulin-sparing effect of exercise resulted in a further enhancement of tissue sensitivity to insulin. GH levels were suppressed by IGF-I treatment at rest, but were still stimulated by exercise. In conclusion, IGF-I has positive inotropic effects in man. Further investigation of the potential role of IGF-I in cardiac conditions such as heart failure appears to be warranted.