Metabolic and hormonal responses to exercise in the anti-obese Lou/C rats
2004
Couturier, K. | Servais, S. | Koubi, H. | Sempore, B. | Cottet-Emard, J.M. | Guigas, B. | Lavoie, J.M. | Favier, R.
OBJECTIVE: Lou/C rats are a substrain of Wistar rats that exhibit a spontaneous low caloric intake and no development of obesity with age. Recently, we reported that Lou/C rats, compared to equally food-restricted Wistar counterparts, show lower resting levels of plasma glucose, epinephrine and liver glycogen. To further explore this metabolic particularity, we used exercise (swimming 60 min) as a situation of high-energy demand, to test the ability of Lou/C rats to maintain euglycemia. DESIGN: Male Lou/C rats (14-week-old) were compared to age-matched male Wistar rats fed either ad libitum (WAL) or Wistar rats whose food was chronically restricted (WFR) to the same caloric intake as the Lou/C rats. RESULTS: In spite of low liver glycogen stores (approximately 50% of normal values), Lou/C rats were able to maintain euglycemia during exercise even though liver glycogen breakdown was blunted. The decreased use of glycogen during exercise in Lou/C rats was associated with a reduced epinephrine response compared to WFR animals. By contrast, WFR were also able to maintain euglycemia during exercise but at the expense of a significant (P < 0.01) decrease in liver and muscle glycogen content. Plasma free fatty acid and glycerol concentrations were increased (P < 0.01) similarly in all three groups during exercise. In a separate experiment conducted in isolated hepatocytes from 24 h fasted Lou/C and Wistar rats, it was found that gluconeogenic flux from glycerol was found to be significantly (P < 0.01) higher in Lou/C than in Wistar rats (5.4 +/- 0.2 vs 3.7 +/- 0.1 micromol/min/g dry cells). Resting and exercising plasma leptin levels were also significantly (P < 0.05) lower in Lou/C than in the two other groups. CONCLUSION: It is concluded that Lou/C rats have the particularity to rely spontaneously less on their liver glycogen stores to meet their energy demands during exercise while maintaining euglycemia.
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