Effect of graded hypoxia on the rat hepatic tissue oxygenation and energy metabolism monitored by near-infrared and 31P nuclear magnetic resonance spectroscopy

Alteration in hepatic cellular adenosine triphosphate (ATP) levels has been shown to be a sensitive index for hypoxic damage. Hepatic ATP metabolism can be monitored by P-31 nuclear magnetic resonance (NMR). Near-infrared spectroscopy (NIRS) can measure tissue oxyhemoglobin (HbO(2)), deoxyhemoglobin (Hb), and cytochrome oxidase (Cyt Ox), which reflect ATP production. In this study, hepatic oxygenation parameters have been correlated with ATP metabolism under graded hypoxia. Sprague-Dawley rats underwent laparotomy for liver exposure. NIRS probes and an NMR coil were placed on the liver and the animal was positioned in the NMR magnet. Graded hypoxia was achieved by a stepwise reduction of the fraction of inspired oxygen (FiO(2)) from 15 to 4%. Recovery between the hypoxic periods was achieved using 30% oxygen. Hepatic tissue oxygenation parameters were measured continuously by NIRS; P-31-NMR spectra obtained at 1 min intervals from energy metabolites and intracellular pH were calculated. All the hypoxic grades produced an immediate reduction in HbO(2) with a simultaneous increase in Hb. Cyt Ox was reduced significantly only with FiO(2) of less than or equal to 10%. P-31-NMR spectra showed a significant decrease in cellular beta nucleoside triphosphate (beta -NTP) only with FiO(2) of less than or equal to 10%. Significant correlation was seen between beta -NTP and HbO(2) (r=0.85), Hb (r=-0.74), and Cyt Ox (r=0.81). Cyt Ox was reduced with intracellular hypoxia and correlated temporally with the reduction of cellular beta -NTP, and therefore could be used as an index for the changes in beta -NTP with hypoxia.