31P NMR studies of energy metabolism in perfused rat kidney.

Conventional biochemical analyses have demonstrated significant alterations in high-energy phosphate metabolism during shock, but the time course of these changes cannot be followed in individual animals because these analyses are invasive and destructive. This study sought to evaluate the utility of 31P NMR as a means of following phosphorus metabolites under various conditions, including those designed to model the shocked state. Twenty adult albino rats were subject to a modified Wiggers' model of hemorrhagic shock lasting from 5 to 140 min. ATP was determined on extracts of the kidneys of each animal both by a biochemical assay and by integration of 31P NMR resonance signals. The equation for renal ATP content plotted versus time for enzymatically determined ATP was 1.79 - 0.0097x (r = 0.83, P less than 0.01) as compared to 1.76 - 0.0093x (r = 0.69, P less than 0.01) for NMR-determined ATP. Isolated, normal rat kidneys perfused with oxygenated, modified Krebs' solution while in the NMR spectrometer maintained normal ATP levels for several hours. ATP/ADP ratios were greater than those observed by conventional enzymatic analysis. Temporary anoxia, induced by substituting 100% N2 for 95% O2:5% CO2, resulted in decreases in ATP content, which reverted to normal with reinstitution of oxygenation. Intracellular pH changed in accordance with perfusate pH during anoxia. It is concluded that 31P NMR studies of the perfused rat kidney have immediate application for the nondestructive study of energy metabolism in shock and ischemia.