Evidence for metabolic regulation of pancreatic glucagon secretion by L-glutamine.
To investigate effects by L-glutamine on pancreatic A-cell secretion and intermediary metabolism, isolated pancreatic islets from normal and streptozotocin treated guinea pigs (A-cell rich islets) were incubated in the presence of glucose (5.5 mM) +/- L-glutamine (10 mM). Glutamine significantly enhanced glucagon release from 297 +/- 54 to 528 +/- 53 pg/micrograms DNA/h in normal islets and from 553 +/- 31 to 806 +/- 50 pg/micrograms DNA/h in A-cell rich islets. All results were expressed on the basis of islet DNA concentration, being 66 +/- 4 ng DNA per normal islet and 32 +/- 2 ng DNA per A-cell rich islet. Simultaneously, glutamine suppressed glucose oxidation to 64 per cent in normal islets and to 47 per cent of basal oxidation in A-cell rich islets. Islet content of ATP was also reduced by glutamine to about 60 per cent in A-cell rich islets, but not significantly changed in normal islets. Glutamine oxidation, at 5.5 mM-glucose, was considerably higher in A-cell rich islets (911 +/- 65 pmol/micrograms DNA/h) than in normal islets (313 +/- 52 pmol/micrograms DNA/h). Addition of porcine insulin (25 mU/ml) counteracted these effects by glutamine, i.e. suppressed glucagon release but increased glucose oxidation and ATP content of the A-cell rich islets. The present findings demonstrate that glutamine stimulates glucagon release and is readily metabolized by the A-cells. Furthermore, the regulation of glucagon secretion by glutamine appears to be reciprocally related to factors affecting glucose metabolism and ATP-levels in the A-cell.
Ostenson
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Grebing
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D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D005934:Glucagon / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism; D005973:Glutamine / Q000378:metabolism / Q000494:pharmacology*; D006168:Guinea Pigs; D007515:Islets of Langerhans / Q000378:metabolism*; D008297:Male; D010084:Oxidation-Reduction; D013311:Streptozocin / Q000494:pharmacology
D005973:Glutamine; D013311:Streptozocin; D000255:Adenosine Triphosphate; D005934:Glucagon; D005947:Glucose