Effects of L-leucine on palmitate metabolism and insulin release by isolated islets of fed and starved rats.

The occurrence of lipid metabolic changes associated with L-leucine (10 mM) stimulation of insulin release was investigated in isolated islets from either fed or starved rats. L-Leucine-stimulated secretion was potentiated by 3 mM glucose and/or 0.5 mM palmitate and was unaffected by 48 h of starvation. Islet palmitate oxidation showed a maximum rate at 3 mM glucose, and starvation increased it almost 2-fold. Regardless of the nutritional state, L-leucine strongly reduced the oxidation of palmitate and increased its incorporation into islet triacylglycerols and phospholipids at 3 mM glucose. This shift of fatty acid metabolism toward esterification might play a role in the mechanism of potentiation of the islet secretory response to L-leucine by glucose and palmitate.