Figure 1.

¹³C NMR spectra of a representative perfused liver from an ob/ob mouse treated chronically with leptin in vivo. No leptin was added during perfusion of the liver. Three spectra measured at the indicated times postsubstrate are shown. The 105–60 ppm region contains signals of newly synthesized ¹³C-labeled glucose and glycogen, which increased monotonically as the level of substrate, seen as [2-¹³C]alanine, was held approximately constant. The ¹³C natural abundance background spectrum of the liver, measured under identical conditions before addition of substrate, was subtracted from each of the spectra shown. (A) C-1 of glucosyl units in glycogen. (B and C) C-1 of β and α anomers of glucose, respectively. (D) C-2 to C-5 of glucosyl units in glycogen. (E) Lactate C-2 and C-2 of the glycerol backbone of triacylglycerols (TG). (F) C-1 + C-3 of TG glycerol. (G) C-6 of glucose and of glucosyl units of glycogen. (H) Glutamate C-2. (I) Glutamine C-2. (J) Alanine C-2. Label in TG glycerol arises from both exchange into endogenous pools and synthesis.