MECHANISM OF GLUCONEOGENESIS INHIBITION IN RAT HEPATOCYTES ISOLATED AFTER IN-VIVO HYPOXIA

Gluconeogenesis was studied in hepatocytes isolated from fasted rats s ubmitted to 24 h of hypoxic exposure (inspired Oz fraction 0.1) or to room air. Hepatocytes from hypoxic rats compared with controls exhibit ed a lower gluconeogenic rate with lactate (5.1 +/- 0.3 vs. 7.2 +/- 0. 3 mu mol . min(-1). g dry cells(-1), P < 0.001) but not with dihydroxy acetone (9.1 +/- 0.3 vs. 9.4 +/- 0.4 mu mol . min(-1). g dry cells(-1) ), suggesting involvement of the phosphoenolpyruvate-pyruvate cycle. E xperiments with perifused hepatocytes from hypoxic and control rats sh owed a single relationship between phosphoenolpyruvate and glucose flu x (J(Glc)) but two different curves when cytosolic oxalacetate was plo tted against J(Glc) The decreased phosphoenolpyruvate carboxykinase (P EPCK) activity in the hypoxic group (9.0 +/- 0.9 vs. 16.2 +/- 1.9 nmol . min(-1). mg protein(-1), P < 001) without change in the Michaelis c onstant further settled the involvement of this step. The significant decrease in PEPCK mRNA levels in livers from hypoxic rats led us to pr opose that in vivo hypoxic exposure inhibits gluconeogenesis at the PE PCK level by decreasing PEPCK gene transcription.