Hepatocytes isolated from the periportal or perivenous zones of livers of fed rats were used to study the long-term (14 h) and short-term (2 h) effects of glucagon on gluconeogenesis and ketogenesis. Long-term culture with glucagon (100 nM) resulted in a greater increase (P less than 0.01) in gluconeogenesis in periportal than in perivenous cells (93 +/- 16 versus 30 +/- 14 nmol/h per mg of protein; 72% versus 30% increase), but short-term incubation (2 h) with glucagon resulted in similar stimulation in the two cell populations. Rates of ketogenesis (acetoacetate and D-3-hydroxybutyrate production) were not significantly higher in periportal cells cultured without glucagon, compared with perivenous cells. However, after long-term culture with glucagon, the periportal cells had a significantly higher rate of ketogenesis (from either palmitate or octanoate as substrate), but a lower 3-hydroxybutyrate/acetoacetate production ratio, suggesting a more oxidized mitochondrial NADH/NAD+ redox state despite the higher rate of beta-oxidation. Periportal hepatocytes had a higher activity of carnitine palmitoyltransferase but a lower activity of citrate synthase than did perivenous cells. These findings suggest that: (i) glucagon elicits greater long-term stimulation of gluconeogenesis in periportal than in perivenous hepatocytes maintained in culture; (ii) after culture with glucagon, the rates of ketogenesis and the mitochondrial redox state differ in periportal and perivenous hepatocytes.
Diminution of the O2 responsiveness of the glucagon-dependent activation of the phosphoenolpyruvate carboxykinase gene in rat hepatocytes by long-term culture at venous PO2
