The effects of increases in perfusion pressure and direction of perfusion flow (anterograde and retrograde) on hepatic carbohydrate metabolism were examined in the isolated perfused rat liver. Changing the direction of flow from anterograde (portal to caval vein) to retrograde (caval to portal vein) increased the rates of glycogenolysis and gluconeogenesis from sorbitol, lactate, pyruvate, and dihydroxyacetone. The extent of stimulation of gluconeogenesis by norepinephrine was higher during anterograde perfusion while stimulation by glucagon was higher during retrograde perfusion. Since the inflowing perfusion pressure was higher in retrograde perfusion (3.8 mmHg) than during anterograde perfusion (2.2 mmHg), we examined the effect of elevation in perfusion pressure on hepatic metabolism. In anterograde (portal to caval vein) perfusion, increases in perfusion pressure above the basal level (2.2 mmHg) caused increases in rates of glycogenolysis and gluconeogenesis with maximum rates at 4 mmHg. The extent of stimulation of gluconeogenesis by norepinephrine decreased and that by glucagon increased during perfusion at elevated pressure. At the same perfusion pressure (4 mmHg), there were no differences in rates of glycogenolysis and gluconeogenesis and in the responses to hormones between anterogradely and retrogradely perfused livers. The omission of Ca2+ ions from the perfusate abolished the effects of retrograde perfusion and of the elevation of perfusion pressure on carbohydrate metabolism. An infusion of A23187 (30 nM) induced an increase in both glycogenolysis and gluconeogenesis with unchanged perfusion pressure. The results suggest that elevated perfusion pressure during retrograde perfusion stimulates hepatic carbohydrate metabolism via a Ca(2+)-dependent process.