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

Abstract

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 O2 supply was found in lambs with aortopulmonary left-to-right shunts. To determine whether the lower systemic O2 supply results in increased anaerobic metabolism, we used [1-13C]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 O2consumption (V˙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 (Ra) and disappearance (Rd) of lactate were similar in shunt and control lambs, both at rest (lactate: 1,201 ± 76 vs. 1,214 ± 151 μmol/l; Ra = Rd: 12.97 ± 1.71 vs. 12.55 ± 1.25 μmol ⋅ min−1 ⋅ kg−1) and during a similar relative workload. We found a positive correlation between Ra and systemic blood flow, O2 supply, andV˙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˙o 2, despite a lower systemic O2supply.