Lactate kinetics at rest and during exercise in lambs with aortopulmonary shunts

In a previous study [G. C. M. Beaufort-Krol, J. Takens, M. C. Molenkamp, G. B. Smid, J. J. Meuzelaar, W. G. Zijlstra, and J. R. G. Kuipers. Am. J. Physiol. 275 (Heart Circ. Physiol. 44): H1503-H1512, 1998], a lower systemic O-2 supply was found in lambs with aortopulmonary left-to-right shunts. To determine whether the lower systemic O-2 supply results in increased anaerobic metabolism, we used [1-C-13]lactate to investigate lactate kinetics in eight 7-wk-old lambs with shunts and eight control lambs, at rest and during moderate exercise [treadmill; 50% of peak O-2 consumption ((V) over dot O-2)]. The mean left-to-right shunt fraction in the shunt lambs was 55 +/- 3% of pulmonary blood flow. Arterial lactate concentrations and the rate of appearance (R-a) and disappearance (R-d) Of lactate were similar in shunt and control lambs, both at rest (lactate: 1,201 +/- 76 vs. 1,214 +/- 151 mu mol/l; R-a = R-d: 12.97 +/- 1.71 vs. 12.55 +/- 1.25 mu mol.min(-1).kg(-1)) and during a similar relative workload. We found a positive correlation between R-a and systemic blood flow, O-2 supply, and (V) over dot O-2 in both groups of lambs. In conclusion, shunt lambs have similar lactate kinetics as do control lambs, both at rest and during moderate exercise at a similar fraction of their peak (V) over dot O-2, despite a lower systemic O-2 supply.