Role of fetal insulin in glycogen metabolism in the liver of the rat fetus.

In the near-term rat fetus liver, insulin decreased phosphorylase a activity, slightly increased synthase a activity and increased both glycogen content and 14C-glucose incorporation into glycogen; anti-insulin serum increased phosphorylase a activity and decreased glucose incorporation but did not modify synthase a activity. When pregnant rats were previously rendered hypoglycemia, insulin injection to the fetus enhanced glycogen accumulation. It is concluded that insulin is a regulatory factor of secondary importance for liver glycogen storage through its action on phosphorylase activity.