Using isolated rat hepatocytes, we studied the effect of epidermal growth factor (urogastrone) (EGF-URO) on the incorporation of [3-14C]pyruvate into glucose and glycogen, on the incorporation of [U-14C]glucose into glycogen, and on the oxidation of [U-14C]glucose to 14CO2. The effects of EGF-URO were compared with those of glucagon and insulin. EGF-URO, with an EC50 of 0.2 nM, enhanced by 34% (maximal stimulation) the conversion of [3-14C]pyruvate into glucose; no effect was observed on the oxidation of glucose to CO2 and on the incorporation of either pyruvate or glucose into glycogen. The effect of EGF-URO on pyruvate conversion to glucose was observed only when hepatocytes were preincubated with EGF-URO for 40 min prior to the addition of substrate. Glucagon (10 nM) increased the incorporation of [3-14C]pyruvate into glucose (44% above control); however, unlike EGF-URO, glucagon stimulated gluconeogenesis better without than with a preincubation period. Neither insulin nor EGF-URO (both 10 nM) affected the incorporation of [U-14C]glucose into glycogen during a 20-min incubation period. However, at longer time periods of incubation with the substrate (60 instead 20 min), insulin (but not EGF-URO) increased the incorporation of [14C]glucose into glycogen; EGF-URO counteracted this stimulatory effect of insulin. In contrast with previous data, our work indicates that EGF-URO can, under certain conditions, counteract the effects of insulin and, like glucagon, promote gluconeogenesis in isolated rat hepatocytes.Key words: rat hepatocytes, EGF-URO, gluconeogenesis, glycogen synthesis.
Characterization of insulin-like actions of anti-insulin receptor antibodies. Effects on insulin binding, insulin degradation, and glycogen synthesis in isolated rat hepatocytes.
