GLUCOSE, PYRUVATE AND LACTATE EFFLUX BY THE PERFUSED LIVER OF A TELEOST, CLARIAS-BATRACHUS DURING ANISO-OSMOTIC EXPOSURE

Glucose, lactate and pyruvate efflux by the perfused liver of the walk ing catfish, Clarias batrachus was studied during anise-osmotic exposu re. During hypo-osmotic exposure (- 80 mOsmol l(-1), maintained with N aCl), glucose, lactate and pyruvate efflux by the perfused liver signi ficantly decreased by 55, 19 and 16%, respectively. During hyper-osmot ic exposure (+ 80 mOsmol l(-1), maintained with NaCl), efflux increase d by 57, 12 and 18%, respectively. Similar effects of glucose, lactate and pyruvate efflux by the perfused liver was also seen when the anis otonicity of the medium was adjusted with mannitol instead of NaCl. Th e decrease of glucose, lactate and pyruvate efflux during hypo-osmotic exposure was correlated with the stimulation of glycogen synthesis an d the reverse was true during hyper-osmotic exposure. These observatio ns were supported by changes in glycogen phosphorylase a (GPase a) and glycogen synthase a (GSase a) activities. During hypo-osmotic exposur e (- 80 mOsmol l(-1)), the GPase a activity decreased by 1.93 fold and GSase a activity increased by 1.63 fold, while during hyper-osmotic e xposure (+ 80 mOsmol l(-1)), the GPase a activity increased by 1.58 fo ld and GSase a activity decreased by 1.95 fold. The total activity of both the enzymes were not effected by a short term exposure to anise-o smotic conditions, suggesting that the alterations in GPase a and GSas e a activity were mainly due to changes of their phosphorylation statu s during anise-osmotic exposure. A direct correlation exists between g lucose efflux and the hydration status of the perfused liver. These al terations of glucose metabolism are probably necessary by this walking catfish to meet the different energy demand, and also for maintenance of glucose homeostasis under osmotic stress. (C) 1998 Elsevier Scienc e Inc. All rights reserved.