Inter-relations between the phospholipids of rat pancreatic islets during glucose stimulation, and their response to medium inositol and tetracaine.

1. Isolated rat pancreatic islets subjected to an increase in glucose concentration from 0.5 to 3 mg/ml showed an increased insulin secretion and 32P-labelling of their phospholipids, especially of phosphatidylinositol, phosphatidylethanolamine, phosphatidylglycerol, and CDP diglyceride. Neither fructose or inositol produced a similar effect. 2. The enhanced labelling of CDP diglyceride and phosphatidylglycerol was suppressed by adding inositol (0.1 mg/ml), while the phosphatidylinositol labelling was increased still further. 3. Tetracaine (0.5 mM), an antagonist of insulin secretion, inhi-ited phosphatidylinositol synthesis while phosphatidylglycerol, CDP diglyceride and phosphatidic acid formation were markedly increased. These effects on phospholipid synthesis were substantially reversed by adding inositol to the medium. Tetracaine also prevented the catabolism of phosphatidylinositol in prelabelled islets but this inhibiton was not reversed by inositol. 4. Inositol addition did not affect insulin secretion in glucose-stimulated islets nor secretion in tetracaine-treated islets. This need not exclude a possible role for heightened phosphatidylinositol cleavage in stimulated insulin secretion.