Effects of varying hematocrit on intestinal oxygen uptake in neonatal lambs
Holzman, I.R.; Tabata, B.; Edelstone, D.I.
American Journal of Physiology 248(4 Pt 1): G432-G436
1985
ISSN/ISBN: 0002-9513 PMID: 3985148 Document Number: 253495
Newborn lambs (15) (9.5 .+-. 2.8 days) were catheterized and intestinal blood flow (.ovrhdot.Qi) measured by the radionuclide microsphere technique at hematocrit levels ranging from 10 to 55%. Seven animals were made progressively anemic and 8 polycythemic by means of exchange transfusions. Using the Flick principle, intestinal O2 delivery (.ovrhdot.Di O2), O2 consumption (.ovrhdot.Vi O2) and O2 extraction were calculated. Initial base-line values were .ovrhdot.Qi = 195.5 ml.cntdot.min-1.cntdot.100 g intestine-1, .ovrhdot.Di O2 = 22.1 ml.cntdot.min-1.cntdot.100 g-1, .ovrhdot.Vi O2 = 4.8 ml.cntdot.min-1.cntdot.100 g-1 and O2 extraction = 22.5%. As the hematocrit was lowered, .ovrhdot.Di O2 decreased and O2 extraction increased and vice versa when the hematocrit was raised. .ovrhdot.Vi O2 remained constant, but .ovrhdot.Qi did not correlate with changes in hematocrit. However, intestinal blood flow, as a percent distribution of total blood flow, decreased with lower hematocrit levels. At no time was there any evidence of anaerobic metabolism as measured by excess lactate production. The intestines of neonatal lambs are capable of maintaining their metabolic needs over a wide range of O2 availability induced by a changing hematocrit. The primary mechanism is through alteration of O2 extraction. Within the range of these experiments, no critically low O2 availability was attained at which anaerobic metabolism became significant.