Regulation of hepatic fructose 2,6-bisphosphate concentrations and lipogenesis after re-feeding in euthyroid and hyperthyroid rats. A regulatory role for glycogenesis.

The time courses of restoration of fructose 2,6-bisphosphate (Fru-2,6-P2) concentrations and rates of lipogenesis after chow re-feeding were correlated with glycogen concentrations and rates of glycogen synthesis in livers of 48 h-starved euthyroid and hyperthyroid rats. Although a regulatory function for glycogen in the regulation of Fru-2,6-P2 concentrations was excluded, an inverse relationship between rates of glycogenesis and Fru-2,6-P2 concentrations indicated a role for glycogenesis in the suppression of Fru-2,6-P2 concentrations during the early (0-4 h) period of re-feeding. There was also a negative correlation between rates of glycogenesis and lipogenesis, and a positive correlation between glycogen concentrations and the lipogenic rate. Decreased rates of glycogenesis in hyperthyroid rats were associated with increased rates of lipogenesis. The response of Fru-2,6-P2 to changes in the glycogenic rate was modified by hyperthyroidism, although a negative correlation was again observed.