The stimulus-secretion coupling of glucose-induced insulin release. XLVI. Physiological role of L-glutamine as a fuel for pancreatic islets.
Exogenous L-glutamine is actively metabolized in rat pancreatic islets. The rate of L-glutamine deamidation largely exceeds the rate of glutamate conversion to gamma-aminobutyrate and alpha-ketoglutarate. The latter conversion occurs in part by oxidative deamination, and in part by transamination reactions coupled with the conversion of 2-keto acids (pyruvate, oxaloacetate), themselves derived from the metabolism of glutamine, to their corresponding amino acids (alanine, aspartate). An important fraction of malate formed from alpha-ketoglutarate leaves the Krebs cycle and is converted to pyruvate, the process being apparently associated with the induction of a more reduced state in cytosolic redox couples. L-Glutamine abolishes the oxidation of endogenous nutrients is documented by the fact that the glutamine-induced increase in O2 consumption is much lower than expected from the rate of 14CO2 output from islets exposed to L-[U-14C]glutamine, L-Glutamine, although decreasing K+ conductance, fails to stimulate insulin release both in the absence and presence of D-glucose. It is proposed that L-glutamine represents a major fuel for pancreatic islets under physiological conditions.
D000818:Animals; D005227:Fatty Acids / Q000378:metabolism; D005947:Glucose / Q000494:pharmacology*; D005973:Glutamine / Q000378:metabolism*; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000378:metabolism*; D007656:Ketoglutaric Acids / Q000378:metabolism; D007700:Kinetics; D008293:Malates / Q000378:metabolism; D010084:Oxidation-Reduction; D010101:Oxygen Consumption / Q000187:drug effects; D011773:Pyruvates / Q000378:metabolism; D051381:Rats; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
D005227:Fatty Acids; D007328:Insulin; D007656:Ketoglutaric Acids; D008293:Malates; D011773:Pyruvates; D005973:Glutamine; D005680:gamma-Aminobutyric Acid; D005947:Glucose