Net Hepatic Gluconeogenic Amino Acid Uptake in Response to Peripheral versus Portal Amino Acid Infusion in Conscious Dogs

Abstract

These studies were conducted to determine the effect of route of gluconeogenic amino acid delivery on the hepatic uptake of the amino acids. After a sampling period with no experimental intervention (basal period), conscious dogs deprived of food for 42 h received somatostatin, intraportal infusions of insulin (3-fold basal) and glucagon (basal), and a peripheral infusion of glucose to increase the hepatic glucose load 1.5-fold basal for 240 min. A mixture of alanine, glutamate, glutamine, glycine, serine and threonine was infused intraportally at 7.6 μmol · kg−1 · min−1 (PorAA group, n = 6) or peripherally at 8.1 μmol · kg−1 · min−1 (PerAA, n = 6), to match the hepatic load of gluconeogenic amino acids in PorAA. During the infusion period, there were no differences in PerAA and PorAA, respectively, with regard to arterial plasma insulin (144 ± 18 and 162 ± 18 pmol/L), glucagon (51 ± 8 and 47 ± 11 ng/L), hepatic glucose load (199.8 ± 22.2 and 210.9 ± 16.6 μmol · kg−1 · min−1), net hepatic glucose uptake (2.8 ± 2.2 and 2.2 ± 1.7 μmol · kg−1 · min−1), hepatic load of amino acids (68 ± 14 and 62 ± 7 μmol · kg−1 · min−1), or net hepatic glycogen synthesis (11.1 ± 2.2 and 8.9 ± 2.2 μmol · kg−1 · min−1). The net hepatic uptake of glutamine (2.1 ± 0.4 vs. 0.8 ± 0.3 μmol · kg−1 · min−1) and the net hepatic fractional extractions of glutamine (0.11 ± 0.02 vs. 0.05 ± 0.02) and serine (0.41 ± 0.03 vs. 0.34 ± 0.02) were greater in PorAA than in PerAA (P < 0.05). We speculate that one or more of the amino acids in the mixture causes enhancement of the net hepatic uptake and fractional extraction of glutamine, and perhaps other gluconeogenic amino acids, during intraportal amino acid delivery.