DIET DIFFERENTIALLY REGULATES GLUCOKINASE AND L-TYPE PYRUVATE-KINASE GENE-EXPRESSION IN RAT-LIVER

The regulation of gene expression of glucokinase (GK) and L-type pyruv ate kinase (L-PK) in rat liver was investigated and compared with the previously reported regulation of lipogenic enzymes. Experiments were conducted in which the time courses and responses to diet quantity of mRNA concentrations and enzyme activities after refeeding a carbohydra te/protein diet (CP) to food-deprived rats were measured. The effects of dietary nutrients on the gene expression were investigated in rats refed either the CP diet, a carbohydrate diet without protein (C), a p rotein diet without carbohydrate (P), or a carbohydrate/protein/corn o il diet (CPF). The effects of the CPF diet on the gene expression afte r insulin treatment to diabetic rats were also Investigated. After ref eeding the CP diet, GK mRNA concentration and enzyme activity reached maximum levels in 2 h and 16-24 h, respectively, whereas those of L-PK peaked in 16 h and 48 h, respectively, similar timecourse to lipogeni c enzymes. Moreover, GK mRNA concentrations were maximal in rats fed 2 0% of the ad libitum diet intake, and L-PK mRNA concentrations, like l ipogenic enzyme mRNA, were maximal in rats fed similar to 50% of ad li bitum intake. GK mRNA concentrations were significantly increased in p arallel with an increase in plasma insulin and glucose concentrations. GK and L-PK mRNA and enzyme levels in rats fed the C diet were compar ably induced to the levels in those fed the CP diet. L-PK mRNA inducti on by the CP diet was significantly reduced by dietary polyunsaturated fatty acids (CPF diet), whereas the GK mRNA induction was not signifi cantly reduced. However, both L-PK and GK mRNA induction by insulin tr eatment of diabetic rats was significantly reduced by dietary polyunsa turated fatty acids (CPF). Thus, L-PK gene expression, similar to lipo genic enzyme gene expression was regulated by dietary nutrients, but G K gene expression was more rapidly regulated by a lesser quantity of d ietary carbohydrate.