Metabolic effects and distribution space of flufenamic acid in the isolated perfused rat liver

The following aspects were investigated in the present work: (a) the action of flufenamic acid on hepatic metabolism (oxygen uptake, glycolysis, gluconeogenesis, uricogenesis and glycogenolysis), (b) the action of flufenamic acid on the cellular adenine nucleotide levels, and (c) the transport and distribution space of flufenamic acid in the liver parenchyma. The experimental system was the isolated perfused rat liver. Perfusion was accomplished in an open, non-recirculating system. The perfusion fluid was Krebs/Henseleit-bicarbonate buffer (pH 7.4), saturated with a mixture of oxygen and carbon dioxide (95:5) by means of a membrane oxygenator and heated to 37 degrees C. The distribution space of flufenamic acid was measured by means of the multiple-indicator dilution technique with constant infusion (step input) of [3H]water plus flufenamic acid. The results of the present work indicate that the metabolic effects of flufenamic acid are the consequence of an uncoupling of oxidative phosphorylation, a conclusion based on the following observations: (a) flufenamic acid increased oxygen uptake, a common property of all uncouplers; (b) the drug also increased glycolysis and glycogenolysis in livers from fed rats (these are expected compensatory phenomena for the decreased mitochondrial ATP formation); (c) flufenamic acid inhibited glucose production from fructose, an energy-dependent process; (d) the cellular ATP levels were decreased by flufenamic acid whereas the AMP levels were increased; and (e) the total adenine nucleotide content was decreased by flufenamic acid and uric acid production was stimulated. Indicator-dilution experiments with flufenamic acid revealed that this substance undergoes flow-limited distribution in the liver and that its apparent distribution space greatly exceeds the aqueous space of the liver. Flufenamic acid changed its behaviour when the portal concentration was increased from 25 to 50 microM. At 25 microM the initial upslope of the outflow profile clearly preceded that of all other concentrations. From the trend of the curves obtained with 50, 100 and 250 microM, one would expect an initial upslope situated at the right of the 50-microM curve. Furthermore, the time of appearance of flufenamic acid in the outflowing perfusate was practically the same irrespective of the portal concentration. For theoretical reasons one would expect progressively longer appearance times when the portal concentration was decreased. It is possible that the amount of flufenamic acid bound to the cell membranes during the early stages of the infusion produced changes that enabled these structures to bind a larger quantity of the drug than originally possible.