Oxygen consumption by the gastrointestinal tract and liver in conscious newborn lambs. 
We determined blood flow to and O2 consumption (VO2) by the gastrointestinal tract (GI) and liver and also measured cardiac output and whole-body VO2 in nine chronically catheterized unanesthetized lambs (7-16 days of age).  Blood flows were calculated with the radionuclide-labeled microsphere technique, and blood O2 contents were measured with an O2 content analyzer.  During the fasting state, GI blood flow was 58 +/- 4 (means +/- SE) ml.min-1.kg body wt-1; GI VO2 was 1.4 +/- 0.1 ml O2.min-1.kg-1.  Neonatal GI VO2 was linearly related to both GI blood flow and O2 delivery (DO2).  GI O2 extraction [(VO2/DO2).100] averaged 28% and did not vary with blood flow or DO2.  Liver blood flow was 73 +/- 4 ml.min-1.kg-1 (271 +/- 23 ml.min-1.100 g liver-1), and liver VO2 was 2.0 +/- 0.1 ml O2.min-1.kg-1 (7.3 +/- 0.5 ml O2.min-1.100 g-1).  Hepatic O2 extraction varied from 18 to 81% .  VO2 by the neonatal liver did not correlate with liver blood flow or DO2.  Hepatic O2 extraction, however, was inversely related to liver DO2.  Our data indicate that the gastrointestinal tract and liver of the unanesthetized newborn animal exhibit O2 demands 1.5-3 times those reported in the adult.  The neonatal gastrointestinal tract meets its O2 demands with a comparatively large blood flow and O2 delivery, whereas the neonatal liver provides for its O2 requirements by varying its O2 extraction.