BLOOD-FLOW TO AND THE METABOLISM OF GLUCOSE AND LACTATE BY THE LIVER INVIVO IN FETAL, NEWBORN AND ADULT SHEEP

1. The blood flow to the liver in fetuses near to term, in newborn and in adult sheep was measured in vivo by the Fick principle using radionuclide-labelled plastic microspheres and timed withdrawal of reference organ blood samples. 2. There is a rapid flow of blood, 410.1 +/- 41.8 ml min-1 (100 g liver)-1, mean +/- S.E.M., to the liver in the fetus. Immediately after birth the blood flow is significantly less (172.5 +/- 27.5 ml min-1 (100 g liver)-1), reflecting the loss of the umbilical venous return to the liver following delivery and separation from the placenta. Arterial blood flow to the liver per unit weight of liver was small in the fetus (9.5 +/- 1.2 ml min-1 (100 g liver)-1), significantly greater in the immediate newborn (27.9 +/- 7.9 ml min-1 (100 g)-1) but appeared to decline with age after birth to 12.2 +/- 6.6 ml min-1 (100 g)-1 in lambs at 16 weeks of age. Portal blood flow to the liver, on a weight basis, changed little with age being 126 +/- 20.9 ml min-1 (100 g liver)-1 in the fetus, 144.7 +/- 21.1 ml min-1 (100 g liver)-1 in the immediate newborn and 203.2 +/- 27.8 ml min-1 (100 g liver)-1 in the adult. 3. Oxygen consumption and glucose and lactate fluxes across the sheep liver were determined from 132 days of gestation into adulthood. 4. The oxygen consumption by the fetal liver was 0.11 +/- 0.02 mmol min-1 (100 g)-1 which represents about 6% of the total fetal oxygen metabolism. Immediately after birth there was an apparent increase in liver oxygen consumption but the wide variation in the values recorded means that the change is not statistically significant. There were no significant changes in liver oxygen consumption with age after delivery, oxygen consumption by the adult liver was 0.16 +/- 0.05 mmol min-1 (100 g)-1. 5. The liver at all ages studied consumed lactate. Lactate consumption was particularly high in the fetus (0.13 +/- 0.04 mmol min-1 (100 g)-1 and could account for three times the oxygen consumed by the fetal liver, but the fate of this lactate is not yet known. 6. In the fetus the liver is in approximately zero glucose balance; in contrast postnatal animals release glucose from the liver at rest. The glucose output from the liver after birth (0.20 +/- 0.05 mmol min-1 (100 g)-1) remained high for at least 4 h after delivery and is sufficient to meet the metabolic requirements of the newborn during the transition period between placental and enteral nutrition.