In vivo Effects of Insulin-Like Growth Factor I in Rats

The scarcity of somatomedin/insulin-like growth factor (SM/IGF) has prevented investigation of the mechanism of SM/IGF action. Recently insulin-like growth factor I (IGF-I) has been synthesized by recombinant DNA technology. With the availability of large quantities of the biosynthetic IGF-I, we undertook a study of biological effects of IGF-I in vivo in rats. 120μg/day of IGF-I was administered continuously for 7 days via subcutaneous implanted osmotic minipump to hypophysectomized (hypox), normal, and diabetic rats. The body weights and tibial epiphyseal widths after 7 day treatment of IGF-I in both hypox and normal rats were significantly greater than those for untreated rats. Blood urea nitrogen levels in both hypox and normal rats treated with IGF-I were significantly lower than those for untreated rats, suggesting that IGF-I has anabolic action in vivo. In contrast to hypox and normal rats, in diabetic rats, IGF-I treatment did not stimulate growth in vivo, but, had a little anabolic and insulin-like effects in vivo.This study demonstrates that IGF-I has growth promoting, anabolic and insulin-like effects in vivo and suggests that IGF-I might be useful in the treatment of growth retardation but not that for diabetes mellitus.