Metabolic responses to moderate exercise in lambs with aortopulmonary shunts

In a previous study we found, after an overnight fast of 18 hours, a lower arterial glucose concentration and a depressed glycogenolysis in lambs with aortopulmonary left-to-right shunts. During exercise, glucose and free fat ty acids (FFA) concentrations normally increase. The aim of this study was to investigate whether the shunt lambs could compensate for a depressed gly cogenolysis by increasing gluconeogenesis and by increasing levels of blood substrates such as FFA and glycerol during exercise. Therefore, we investi gated glucose kinetics, with [U-C-13]glucose, in five 7-week-old shunt and 7 control lambs of a similar age, at rest and during moderate exercise (tre admill; 50% of (V) over dot o(2) peak). The glucose production rate and the rate of disappearance of glucose were lower in shunt than in control lambs , both at rest and during exercise. We found no difference in metabolic cle arance rate of glucose, glucose recycling, or gluconeogenesis between both groups of lambs. Glycogenolysis was at rest lower in shunt than in control lambs and tended to be lower during exercise. The arterial concentrations o f pyruvate, lactate, FFA, and total and free glycerol increased during exer cise in both groups of lambs. In conclusion, shunt lambs have lower arteria l glucose concentrations than control lambs, both at rest and during modera te exercise. This was due to a lower glucose production rate, in particular a lower glycogenolysis. In addition, the reduced glycogenolysis rate was n ot offset by an increase in gluconeogenesis nor by an increase in other sub strates that can be utilized by working muscles. Copyright (C) 2001 by W.B. Saunders Company.