31P NMR spectra of 2 typical experiments at the beginning (A1 and B1) and after 115 min of perfusion (A2 and B2). A1 and A2 were 31P NMR spectra from a control rat perfused with Krebs-Henseleit buffer alone and B1 and B2 were 31P NMR spectra from rat perfused with both 30 mM glucose and insulin. Major resonances are assigned to (a) phosphomonoesters, (b) phosphocholine, (c) intracellular inorganic phosphate, (d) glycerol-3-phosphorylcholine, (f) nucleoside-5'-triphosphates (γNTP) and diphosphates (βNDP), (g) α-NTP and α-NDP, (h,i) nicotinamide adenine dinucleotide and uridine-5'-diphosphoglucose, (j) βNTP. The external reference is not shown (18.40 ppm). Note the βATP (j) decrease in the KHB group (A1 and A2) and the relative stability of the ATP content of the liver during the perfusion of both 30 mM glucose and insulin (B1 and B2).