In vivo metabolic action of insulin-like growth factor I in adult rats.

The acute metabolic actions of insulin-like growth factor I were studied in anaesthetized adult rats and its potency was compared to that of insulin. Following an i.v. bolus injection of insulin-like growth factor I a dose-dependent decrease of blood glucose and serum non-esterified fatty acid concentrations was noted with a potency of about 2% that of insulin. Stimulation of total body glucose disposal during euglycaemic clamping required approximately 50 times higher insulin-like growth factor I serum concentrations to achieve an identical half-maximal response. A similar difference in potency was observed for the stimulatory action on 2-deoxyglucose uptake and on glycogen formation in skeletal muscle. Lipogenesis in epididymal fat pads was increased dose-dependently by both hormones requiring approximately 30 times higher half-maximally effective serum concentrations of insulin-like growth factor I. These data demonstrate that insulin-like growth factor I exerted acute insulin-like metabolic actions in vivo with low potency. These effects were probably mediated via insulin receptors. A preferential stimulation of glucose metabolism in skeletal muscle was not observed.