GLUCONEOGENESIS AND GLUCURONIDATION IN LIVER IN-VIVO AND THE HETEROGENEITY OF HEPATOCYTE FUNCTION

In order to examine metabolic zonation in human liver, [2-C-14]glycerol, which labels carbons 2 and 5 of glucose-6-P, and [1-C-14]lactate, which labels carbons 3 and 4 of glucose-6-P, in the process of gluconeogenesis, were infused intravenously into healthy subjects who ingested acetaminophen and had fasted 36 h. Distributions of C-14 were determined in glucose in blood and in the glucuronic acid moiety of acetaminophen glucuronide excreted in urine. Ratios of C-14 in carbons 2 and 5 to C-14 in carbons 3 and 4 were significantly higher in blood glucose than in glucuronide. Since glucose and glucuronic acid are formed from glucose-6-P in liver without randomization of carbon, the differences in the ratios indicate that the pool of glucose-6-P in liver is not homogeneous. The glucuronide sampled glucose-6-P with more label from lactate than glycerol compared to the glucose-6-P sampled by the glucose. The apparent explanation is the greater decrease in glycerol compared with lactate concentration as blood streams from the periportal to the perivenous zones of the liver lobule. Glucuronidation is then expressed in humans relatively more in the perivenous than periportal zones and gluconeogenesis from glycerol more in the periportal than perivenous zones.