Contribution of insulin to the ascorbate recycling system in the chicken liver

The effect of insulin on the ascorbate recycling system in the chicken liver was examined. First, insulin was injected subcutaneously into the chicken, and liver glutathione-dependent dehydroascorbate reductase (GSH-DHAR) activity was determined. Insulin increased liver GSH-DHAR activity, but did not affect plasma and liver ascorbate concentration. Dehydroascorbate increased plasma and liver ascorbate levels, and liver GSH-DHAR activity. However, distinct changes in plasma insulin level were not observed by dehydroascorbate injection. In addition, reduction of external dehydroascorbate in cultured chicken hepatocytes could not be observed in an insulin-deprived culture, although the cells reduced external dehydroascorbate in a serum-free culture with insulin. We concluded that insulin affects the ascorbate recycling system as an essential factor in the chicken liver.