Interrelationship between aminopyrine oxidation and gluconeogenesis in hepatocytes prepared from fructose-pretreated mice.
Aminopyrine oxidation was studied in isolated hepatocytes prepared from 24-h-starved mice (i) after induction of the NADPH-generating malic enzyme and glucose-6-phosphate dehydrogenase, but not the mixed function oxygenases by fructose, (ii) after induction of both mixed function oxygenases and NADPH-generating malic enzyme and glucose-6-phosphate dehydrogenase by phenobarbital and (iii) without any pretreatment. Phenobarbital pretreatment, as expected, increased the rate of aminopyrine oxidation of isolated hepatocytes. However, fructose pretreatment also enhanced the rate of N-demethylation of aminopyrine by more than 100% supporting the view that the availability of NADPH is rate limiting in drug oxidation under certain conditions. The role of malic enzyme and glucose-6-phosphate dehydrogenase in the NADPH supply for aminopyrine oxidation was investigated by the addition of two groups of gluconeogenic precursors: lactate or alanine and glycerol or fructose with the simultaneous measurement of glucose synthesis and aminopyrine N-demethylation. There was a clear correlation between the increased rate of aminopyrine oxidation and the decreases of glucose production caused by aminopyrine. Gluconeogenesis in the presence of 1 mM aminopyrine was decreased by 70-80% when alanine or lactate were used as precursors, it was decreased by only 35-40% when glucose production was started from glycerol or fructose; in an accordance with the facts that NADPH generation and gluconeogenesis starting from alanine or lactate share two common intermediates--malate and glucose-6 phosphate--, while there is only one common intermediate--glucose-6 phosphate--if fructose or glycerol are used. Similar results were obtained with the addition of the structurally dissimilar hexobarbital. It is concluded that besides malic enzyme, glucose-6-phosphate dehydrogenase also takes part in NADPH supply for drug oxidation in glycogen-depleted hepatocytes.
D000632:Aminopyrine / Q000378:metabolism*; D000818:Animals; D002478:Cells, Cultured; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D005557:Formaldehyde / Q000494:pharmacology; D005632:Fructose / Q000494:pharmacology*; D005943:Gluconeogenesis / Q000187:drug effects*; D006591:Hexobarbital / Q000494:pharmacology; D007700:Kinetics; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D051379:Mice; D008815:Mice, Inbred Strains; D008862:Microsomes, Liver / Q000378:metabolism; D010084:Oxidation-Reduction; D010634:Phenobarbital / Q000494:pharmacology
D000632:Aminopyrine; D005557:Formaldehyde; D005632:Fructose; D003577:Cytochrome P-450 Enzyme System; D006591:Hexobarbital; D010634:Phenobarbital