RATES OF PENTOSE CYCLE FLUX IN PERFUSED RAT-LIVER - EVALUATION OF THE ROLE OF REDUCING EQUIVALENTS FROM THE PENTOSE CYCLE FOR MIXED-FUNCTION OXIDATION

  • 1 January 1985
    • journal article
    • research article
    • Vol. 28  (4) , 371-376
Abstract
Rates of NADPH production via the pentose phosphate cycle were determined in perfused livers from phenobarbital-treated rats by measuring 14CO2 production from [1-14C]glucose infused in the presence and absence of p-nitroanisole (0.2 mM), a substrate for mixed-function oxidation. In the fed state, basal rates of NADPH generation were 34-44 .mu.mol/g/hr. p-Nitroanisole, which was metabolized at rates of 8.9 .mu.mol/g/hr, stimulated pentose cycle-dependent NADPH production by 21-24 .mu.mol/g/hr. Fasting for 24 hr prior to perfusion diminished pentose cycle flux by 80% and largely abolished the stimulation of the pentose cycle by p-nitroanisole. In contrast, rates of p-nitroanisole O-demethylation were only diminished slightly, to 5.7 .mu.mol/g/hr. Fasting decreased hepatic glucose, glucose 6-phosphate, and 6-phosphogluconate contents drastically as expected. Pretreatment of rats with 6-aminonicotinamide, which is metabolized to a potent inhibitor of 6-phosphogluconate dehydrogenase, decreased rates of NADPH generation via the pentose cycle to 6.9 .mu.mol/g/hr but did not alter rates of p-nitroanisole metabolism (8.8 .mu.mol/g/hr). Basal rates of NADPH generation decreased from 38 to 26 .mu.mol/g/hr during infusion of potassium cyanide (2 mM), an inhibitor of mitochondrial energy metabolism. Cyanide also decreased rates of p-nitroanisole O-demethylation by over 60%; however, stimulation of NADPH generation via the pentose cycle by p-nitroanisole was as great in the presence (17-12 .mu.mol/g/hr) as in the absence of cyanide. Since rates of mixed-function oxidation were unaffected after virtually complete inhibition of the pentose cycle with 6-aminonicotinamide, it is concluded that reducing equivalents for the mixed-function oxidation of p-nitroanisole are not provided by the pentose cycle under these conditions.

This publication has 12 references indexed in Scilit: