Similar Dose Responsiveness of Hepatic Glycogenolysis and Gluconeogenesis to Glucagon In Vivo

This study was undertaken to determine whether the dose-dependent effect of glucagon on gluconeogenesis parallels its effect on hepatic glycogenolysis in conscious overnight-fasted dogs. Endogenous insulin and glucagon secretion were inhibited by somatostatin (0.8 μg · kg⁻¹ · min⁻¹), and intraportal replacement infusions of insulin (213 ± 28 (αU kg⁻¹ · min⁻¹) and glucagon (0.65 ng · kg⁻¹ · min⁻¹) were given to maintain basal hormone concentrations for 2 h (12 ± 2 and 108 ± 23 pg/ml, respectively). The glucagon infusion was then increased 2-, 4-, 8-, or 12-fold for 3 h, whereas the rate of insulin infusion was left unchanged. Glucose production (GP) was determined with 3-[³H]glucose, and gluconeogenesis (GNG) was assessed with tracer (U-[¹⁴C]alanine conversion to [¹⁴C]glucose) and arteriovenous difference (hepatic fractional extraction of alanine, FEA) techniques. Increases in plasma glucagon of 53 ± 8, 199 ± 48, 402 ± 28, and 697 ±149 pg/ml resulted in initial (15- 30 min) increases in GP of 1.1 ± 0.4 (N = 4), 4.9 ± 0.5 (N = 4), 6.5 ± 0.6 (N = 6), and 7.7 ± 1.4 (N = 4) mg kg⁻¹ · min⁻¹, respectively; increases in GNG (∼3 h) of 48 ± 19, 151 ± 50, 161 ± 25, and 157 ± 7%, respectively; and increases in FEA (3 h) of 0.14 ± 0.07, 0.37 ± 0.05, 0.42 ± 0.04, and 0.40 ± 0.17, respectively. In conclusion, GNG and glycogenolysis were similarly sensitive to stimulation by glucagon in vivo, and the dose-response curves were markedly parallel.