Glucagon effects on brain carbohydrate and ketone body metabolism of rainbow trout.

Abstract

The levels of glycogen in brain, lactate and acetoacetate in brain and plasma, glucose in plasma and the activities of brain key enzymes of glycogen metabolism (glycogen phosphorylase, GPase, glycogen synthetase, GSase), gluconeogenesis (fructose 1,6-bisphosphatase, FBPase), and glycolysis (6-phosphofructo 1-kinase, PFK) were evaluated in rainbow trout, Oncorhynchus mykiss, from 0.5 to 3 hr after intraperitoneal injection of 1 ml/kg(-1) body weight of saline alone (controls) or containing bovine glucagon at three different doses: 10, 50, and 100 ng/g(-1) body weight. The results obtained demonstrate, for the first time in a teleost fish, the existence of changes in brain carbohydrate and ketone body metabolism following peripheral glucagon treatment. A clear stimulation of brain glycogenolytic potential was observed after glucagon treatment, as judged by the time- and dose-dependent changes observed in brain glycogen levels (up to 88% decrease), and GPase (up to 30% increase) and GSase (up to 42% decrease) activities. In addition, clear time- and dose-dependent increased and decreased levels were observed in brain of glucagon-treated rainbow trout for lactate (up to 60% increase) and acetoacetate (up to 67% decrease), respectively. In contrast, no significant changes were observed after glucagon treatment in those parameters related to glycolytic/gluconeogenic capacity of rainbow trout brain. Altogether, these in vivo results suggest that glucagon may play a role (direct or indirect) in the regulation of carbohydrate and ketone body metabolism in brain of rainbow trout.