Regulation of net hepatic glycogenolysis and gluconeogenesis by epinephrine in humans

Abstract

The relative contributions of net hepatic glycogenolysis (NHG) and gluconeogenesis to rates of glucose production during a physiological increment in plasma epinephrine concentrations, independent of changes in plasma insulin concentrations, were determined in seven fasting, healthy young subjects. Plasma insulin concentrations were kept constant by infusing somatostatin (0.1 μg·kg−1·min−1) and replacing basal insulin (24 pmol·m−2·min−1). Epinephrine (1.2 μg·m−2·min−1) was infused for 90 min while NHG was assessed directly by13C magnetic resonance spectroscopy. The rate of glucose production was assessed using [6,6-2H2]glucose, and gluconeogenesis was calculated as the difference between the rate of glucose production and NHG. Plasma epinephrine concentrations increased rapidly from ∼100 to ∼2,000 pmol/l ( P < 0.00001) accompanied by an increase in plasma glucose concentrations from 4.3 ± 0.2 to 13.3 ± 0.3 mmol/l at 90 min ( P = 0.00001). This increase in plasma epinephrine concentration resulted in a 2.5-fold increase in glucose production (from 14.4 ± 1.0 μmol·kg−1·min−1to 35.7 ± 2.0 μmol·kg−1·min−1, P < 0.0001), which lasted for ∼60 min ( phase 1), after which glucose production decreased to 31.2 ± 1.9 μmol·kg−1·min−1( P < 0.0001 vs. basal) during the last 30 min of the epinephrine infusion ( phase 2). Hepatic glycogen concentrations decreased almost linearly during phase 1, and rates of NHG were 19.9 ± 3.0 μmol·kg−1·min−1( P = 0.005 vs. basal), which could account for ∼60% of glucose production. During phase 2, NHG decreased to 7.3 ± 2.8 μmol·kg−1·min−1( P = 0.02 vs. peak), accounting for only ∼20% of glucose production. In conclusion, in the presence of basal plasma insulin and glucagon concentrations, a physiological increase in plasma epinephrine concentrations stimulates glucose production with an initial, 60-min transient phase caused by stimulation of NHG and a second phase that can mostly be attributed to a twofold increase in rates of gluconeogenesis.