In perifused pancreatic islets, the fluorescence of reduced pyridine nucleotides (NAD(P)H) was measured continuously. Elevation of glucose concentration in the medium from 0-5 mM to 20 mlVl led to an increase in l~AD(P)H-fluorescence beginning 10-20 sec after change of medium. Perifusion with calcium-free media had no influence on this effect. It was, however, partially or completely blocked by 2-deoxy D-glucose, D-glucosamine, or D-mannoheptulose. D-mannose, but not D-fructose and L-lactate, enhanced ~qAD(P)I-I-fluorescence from pancreatic islets. Pyruvate caused but a small fluorescence increase. From these observations it is concluded that D-glucose leads to the increase of NAD(P)I-i-fluorescence by mediation of the phosphoglyceraldehyde dehydrogenase reaction.
The insulinotropic effects of L-leucine and e-ketoisocaproic acid have been compared in perifused isolated pancreatic islets. In contrast to e-ketoisocaproic acid (10 mM), L-leucine (10 raM) released less insulin in the presence than in the absence of glucose (5 mM). Changes of islet cell metabolism accompanying insulin release were studied by recording the fluorescence of reduced pyridine nucleotides. The traces of L-leucine-or e-ketoisocaproic acid-induced fluorescence increase differed both in the absence and in the presence of glucose (5 mM). When the medium perifusing the islets contained 30 m2Cf L-leucine, a-ketoisoeaproic acid (10 raM) still triggered a significant insulin release. These results argue against an indirect action of e-ketoisocaproie acid via transformation to L-leucine. isocaproic acid (10 mM), Le-hydroxyisocaproic acid (10 mM) or ~-ketoisovaleric acid stimulated no remarkable insulin release, demonstrating that the strong insulinotropie effect of ~-ketoisoeaproic acid is coupled both to its ~-ketogroup and to the length of its carbon chain.
Double blind clinical and laboratory study of hypoglycaemia with human and porcine insulin in diabetic patients reporting hypoglycaemia unawareness after transferring to human insulin.
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