Effects of insulin-like growth factor I on basal and stimulated glucose fluxes in rat liver

Abstract

Effects of insulin-like growth factor I (IGF-I) and insulin on glucose and potassium fluxes were examined by measuring transhepatic glucose and potassium balance in isolated perfused rat livers. At 1nM, both IGF-I and insulin decreased basal glucose release by ≈ 64% (P < 0.05). Adrenaline (epinephrine)-stimulated glucose release (42.6±4.5µmol/g of liver within 30 min) was inhibited (P < 0.05) by ≈ 32 and ≈ 52% during IGF-I and insulin exposure, which was accompanied by reduced cAMP release (-71 and -80%, P < 0.05). IGF-I- and insulin-induced reduction of glucose release only decreased during calcium-free perfusion, but not during inhibition of phosphoinositide 3-kinase by wortmannin. Both IGF-I and insulin induced net potassium uptake, while insulin also attenuated the response to adrenaline. In conclusion, IGF-I causes (i) insulin-like inhibition of hepatic glycogenolysis, even at low, nanomolar concentrations, which is associated with decreased cAMP release, reduced in the absence of Ca2+, but not mediated by phosphoinositide 3-kinase, (ii) reduction of adrenaline-induced glycogenolysis and (iii) net potassium uptake under basal conditions.