Comparison of fetal and maternal hind limb metabolic quotients in sheep

This study compared substrate utilization by the fetal hind limb and the maternal hind limb in 26 sheep at 120 to 135 days of gestation. Catheters were placed in the mother and the fetus to sample femoral arterial and venous blood by use of a nonocclusive technique. Arterial and venous concentrations of oxygen content, glucose, lactate, acetate, and ketoacids were measured simultaneously and were used to calculate metabolic quotients. The fetal hind limb was perfused with arterial blood having a lower oxygen content than the maternal hind limb (3.03 ± 0.17 versus 4.94 ± 0.24 mmol/L, p < 0.001) and had a smaller arteriovenous difference of oxygen content (0.97 ± 0.05 versus 2.68 ± 0.104 mmol/L, p < 0.001). Despite a lower fetal arterial glucose concentration (0.81 ± 0.05 versus 2.58 ± 0.13 mmol/L, p < 0.001), the glucose/oxygen quotient (0.82 ± 0.05 versus 0.20 ± 0.02, p < 0.001) and the arteriovenous difference of glucose (0.13 ± 0.01 versus 0.08 ± 0.01 mmol/L, p < 0.001) were higher in the fetal hind limb than in the maternal hind limb. Both limbs were net producers of lactate. The (glucose + lactate)/oxygen quotient was also higher in the fetal hind limb than in the maternal hind limb (0.68 ± 0.05 versus 0.12 ± 0.04, p < 0.001). In the maternal hind limb, acetate and ketoacids uptake could account for 48% ± 6% of total oxygen consumption whereas in the fetal hind limb it accounted for only 12% ± 4% (p < 0.001). The data demonstrate that, in relation to oxygen uptake, fetal hind limbs have approximately a 2.8% higher rate of perfusion and take up approximately four times as much glucose as the hind limbs of the mother in the resting state.