The stimulus-secretion coupling of amino acid-induced insulin release. Metabolic response of pancreatic islets of L-glutamine and L-leucine.
L-Glutamine markedly enhances insulin release evoked by L-leucine in rat pancreatic islets. The metabolic situation found in the islets exposed to both L-glutamine and L-leucine was investigated. L-Leucine slightly decreased the rate of L-glutamine deamidation, inhibited the conversion of glutamate to 2-ketoglutarate by transamination, increased the oxidative deamination of L-glutamate, stimulated the recirculation of 2-ketoglutarate to glutamate and inhibited the further oxidative metabolism of 2-ketoglutarate. L-Glutamine slightly decreased the rate of L-leucine conversion to 2-ketoisocaproate, but inhibited more severely the conversion of 2-ketoisocaproate to acetoacetate and CO2. Several of these findings appeared attributable to activation of glutamate dehydrogenase by L-leucine. When allowance was made for the influence of exogenous amino acids on the oxidation of endogenous fatty acids, a close parallelism was found between the rate of generation of reducing equivalents or O2 uptake and the insulin secretory response to L-leucine and/or L-glutamine. These findings reinforce the view that the process of nutrient-stimulated insulin release coincides with and may be attributable to an increase in catabolic fluxes in the islet cells.
D000818:Animals; D005973:Glutamine / Q000378:metabolism / Q000494:pharmacology*; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism*; D007930:Leucine / Q000378:metabolism / Q000494:pharmacology*; D008954:Models, Biological; D009243:NAD / Q000378:metabolism; D009249:NADP / Q000378:metabolism; D051381:Rats
D007328:Insulin; D005973:Glutamine; D009243:NAD; D009249:NADP; D007930:Leucine