Glucokinase is highly induced and glucose-6-phosphatase poorly repressed in liver of rainbow trout (Oncorhynchus mykiss) by a single meal with glucose

The low dietary starch utilisation by rainbow trout (Oncorhynchus mykiss) m ay be attributed to a dysfunction of the nutritional regulation of the hepa tic glucose/glucose-6-phosphate cycle. The present study was initiated to a nalyse the regulation of activity and gene expression of hepatic glucokinas e (GK) and glucuse-6-phosphatase (G6Pase) by dietary carbohydrates in this species. We found that even a single meal containing 24% of glucose is suff icient to induce the GK expression (mRNA and activity) as in mammals. In co ntrast, although the inhibitory effect of dietary glucose on G6Pase express ion is observed at the molecular level, the G6Pase activity is not signific antly inhibited by dietary glucose. Thus. in contrast to the gluconeogenic G6Pase enzyme, a rapid adaptation of the hepatic glycolytic GK enzyme to di etary glucose seems effective in rainbow trout. These results suggest that in carnivorous rainbow trout, the liver is capable to strongly regulate the utilisation of glucose but not the synthesis of glucose. (C) 2001 Elsevier Science Inc. All rights reserved.