FFA and insulin response dissociation to gradual short-term food restriction in exercising rats

The present study examines the metabolic and hormonal responses of progressive short-term food restriction in rats at rest and during exercise. The night prior to the experiment, previously cannulated rats were assigned to one of three groups: (A) normal diet, (B) 50% food restriction, and (C) 75% food restriction. They were then run continuously for 50 min at 26 m.min-1, 0% grade. Resting liver glycogen levels were decreased in groups B and C (50% and 92%) while B-hydroxybutyrate values were increased in group C only. A similar group main effect (resting and exercise values) of a significant (P less than 0.05) increase in free fatty acid concentrations was found in groups B and C as compared to group A, while a decrease in insulin (P less than 0.01) and glucose (P less than 0.05) concentrations was observed in group C only. Norepinephrine and epinephrine concentrations were increased similarly in all three groups following exercise. Resting muscle glycogen levels were progressively reduced following food restrictions. These results indicate that (1) food deprivation at rest and during exercise first affects free fatty acid concentrations and thereafter the insulin response, (2) prolonged exercise following food restrictions increases the metabolic adaptative state of the resting organism. These findings are in disagreement with a sole action of pre-exercise insulin as a determinant of metabolic responses to exercise and provide evidence to the concept that a progressive reduction in liver glycogen might constitute a stimulus for the early free fatty acid response.