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.