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 inj ected sc in a cross-over, randomized, double blind fashion into eight healthy male volunteers. Cardiac function and performance were evaluat ed by echocardiography and exercise test. In parallel, the metabolic e ffects of IGF-I during exercise were investigated. IGF-I improved card iac performance with a significant increase in stroke volume and cardi ac output by 14% and 18% (P < 0.03 and P < 0.04), respectively. Ejecti on fraction increased by 9% after IGF-I treatment (P < 0.05). Heart ra te was not significantly increased at rest or during exercise. Systoli c blood pressure was slightly increased by IGF-I, whereas diastolic bl ood pressure was slightly decreased, resulting in a continuous increas e in the blood pressure amplitude at rest and during exercise, but wit hout reaching statistical significance. Maximal exercise duration and peak oxygen consumption were not changed. Exercise was uneventful, wit hout pathological changes on electrocardiogram records. Glucose levels were unchanged, whereas insulin and C peptide levels were decreased b y IGF-I at rest. During exercise, insulin levels were further decrease d, and the insulin-sparing effect of exercise resulted in a further en hancement 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 inves tigation of the potential role of IGF-I in cardiac conditions such as heart failure appears to be warranted.