Glucostat capacity and metabolic zonation in rat liver after portocaval anastomosis.

Abstract

The activities and zonal distribution of key enzymes of carbohydrate metabolism were studied in livers of rats after end-to-side portocaval anastomosis. Sham-operated control animals with the same periods of interruption of hepatic blood supply as the shunted animals were pair-fed. The following alterations were observed: Food uptake was reduced to about 20% at the first postoperational day; it was then increased continuously to about 70% at day 8. Body weight, after a small 10% postoperational decrease, remained unaltered, but liver weight was lowered to 55% at day 8 and then stayed constant. The total glycogen reserves of the liver (g X 100 g body weight-1) were reduced, after a transient fall to about 10% at day 1-4, to about 25%. The total activity of the glucogenic phosphoenolpyruvate carboxykinase (mumol . min-1 X 100 g body weight-1) was diminished, after a transient increase to 190% and 150% at day 1 and 2 respectively, to about 55% from day 8 onwards. The total activity of the glucogenic glucose-6-phosphatase was lowered without a transient rise to about 30%. The total activities of the glycolytic pyruvate kinase isoenzyme L and glucokinase were decreased continuously to about 40% at day 8; that of the citrate cycle enzyme succinate dehydrogenase was lowered parallel with liver weight to 55%. The transient decrease of the glycogen reserves and the intermediate increase of the phosphoenolpyruvate carboxykinase capacity were due to the operational stress, since they were observed also in the sham-operated control animals. All other alterations, the decrease of liver weight and of the capacities of both gluconeogenic and glycolytic key enzymes, were specific for the portocaval anastomosis. The normal periportal to perivenous gradient of phosphoenolpyruvate carboxykinase of about 3.5:1, as measured in microdissected tissue samples, remained the same with specific activities reduced to about 80% each in the two zones. The normal periportal to perivenous gradient of pyruvate kinase L of about 1:1.7 was equalized with levels lowered to 35% and 23%, respectively, in the two zones. The normal periportal to perivenous gradients of glucose-6-phosphatase and succinate dehydrogenase, demonstrated histochemically, were essentially maintained with perivenous bridging occurring transiently at day 4 and 8.(ABSTRACT TRUNCATED AT 400 WORDS)