Hepatic glucokinase is induced by dietary carbohydrates in rainbow trout, gilthead seabream, and common carp

Glucokinase (GK) plays a central role in glucose homeostasis in mammals. Th e absence of an inducible GK has been suggested to explain the poor utiliza tion of dietary carbohydrates in rainbow trout. In this context, we analyze d GK expression in three fish species (rainbow trout, gilthead seabream, an d common carp) known to differ in regard to their dietary carbohydrate tole rance. Fish were fed for 10 wk with either a diet containing a high level o f digestible starch (>20%) or a diet totally deprived of starch. Our data d emonstrate an induction of GK gene expression and GK activity by dietary ca rbohydrates in all three species. These studies strongly suggest that low d ietary carbohydrate utilization in rainbow trout is not due to the absence of inducible hepatic GK as previously suggested. Interestingly, we also obs erved a significantly lower GK expression in common carp (a glucose-toleran t fish) than in rainbow trout and gilthead seabream, which are generally co nsidered as glucose intolerant. These data suggest that other biochemical m echanisms are implicated in the inability of rainbow trout and gilthead sea bream to control blood glucose closely.