[13C]NMR studies of the effect of the somatostatin analogue octreotide on hepatic glycogenesis and glycogenolysis

NMR spectroscopy is a useful tool for monitoring multiple intermediate metabolic pathways in different organs in intact animals and humans. We report the effect of the somatostatin analogue octreotide on the fate of 13C-labeled glucose administered to fasted and well-fed rats as determined by NMR spectroscopy. The production of 13C-labeled glycogen and its subsequent breakdown after the end of infusion was identified with a time resolution of 7 min. Hepatic glycogen synthesis was not different between control and octreotide-treated animals but persisted for 15 min after the end of the infusion only in control animals. Glycogenolysis, however, was initiated immediately after the end of infusion in octreotide-treated animals where the half-life of glycogen was 40 min compared with 68 min in control animals. However, once initiated, the rate of glycogenolysis was not significantly altered by octreotide. Although octreotide had no effect on glucose signal intensities in fasted animals, 13C glucose signals were more intense in octreotide compared with control well-fed animals. In conclusion, octreotide alters rat hepatic metabolism by accelerating the onset of glycogenolysis and stimulating glucose accumulation without significantly interfering with glycogen synthesis.