Glucose, lactate, and beta-hydroxybutyrate utilization by rainbow trout brain: changes during food deprivation.

In order to evaluate the normal (fed conditions) substrate utilization rates of rainbow trout (Oncorhynchus mykiss) brain, CO2 production from glucose, lactate, and beta-hydroxybutyrate was tested in pooled brains. Oxidation rates, as well as the capacity for metabolism of carbohydrate and ketone bodies, were also evaluated in brain of rainbow trout that were food-deprived for 14 d. Under normal (fed) conditions, rainbow trout brain oxidized glucose and lactate at rates higher than those described for mammals; oxidation rates of beta-hydroxybutyrate were lower in rainbow trout brain than those observed for lactate and glucose, and also lower than those described for mammals. Under food-deprivation conditions, glucose and lactate oxidation rates decreased in brains, suggesting the existence of brain metabolic depression, and beta-hydroxybutyrate oxidation rates sharply increased, suggesting increased utilization of ketone bodies.