GLYCOGEN-SYNTHESIS FROM GLUCOSE BY DIRECT AND INDIRECT PATHWAYS IN HEPATOCYTE CULTURES FROM DIFFERENT NUTRITIONAL STATES

The conversion of glucose to glycogen by direct and indirect pathways was determined from the incorporation of [6-H-3,U-C-14]glucose into gl ycogen in hepatocyte cultures isolated from fed, fasted or fasted-refe d rats. Mercaptopicolinate, an inhibitor of phosphoenolpyruvate carbox ykinase (PEPCK) was used to determine the extent by which 6-tritium is lost by mechanisms not involving flux through PEPCK. Glucose conversi on to glycogen was lower in hepatocytes from fasted and higher in hepa tocytes from fasted-refed rats than in hepatocytes from rats fed ad li bitum. Insulin increased glycogen synthesis in hepatocytes from all nu tritional states, and it decreased the H-3/C-14 ratio incorporated int o glycogen. This increased loss of 6-tritium was only in part mercapto picalinate-sensitive. Lactate and pyruvate (2 mM + 0.2 mM) increased g lycogen deposition, largely by stimulation of glucose conversion to gl ycogen by the direct pathway. Insulin-induced glucokinase mRNA express ion was higher in hepatocytes from fed than from fasted or refed rats whereas PEPCK mRNA expression was lowest in hepatocytes from fasted-re fed rats. Hepatocyte cultures derived from different nutritional state s express differences in glycogen synthesis from glucose by direct and indirect pathways as well as differences in the extent by which pyruv ate cycling accounts for loss of 6-tritium.