Studies on chemical mechanisms of the action of neurotransmitters and hormones: I. Relationship between hormone-stimulated 32P incorporation into phosphatidic acid and into phosphatidylinositol in pigeon pancreas slices

Abstract

In pigeon pancreas slices, pancreozymin evoked an increased incorporation of 32P into phosphatidylinositol, phosphatidic acid, phosphatidylethanolamine, and, to a lesser extent, phosphatidylcholine. The pattern of this response is the same as that observed previously in response to acetylcholine. Pancreozymin or acetylcholine did not significantly affect either the uptake of orthophosphate- 32P or the specific activity and levels of nucleotide P̃ in pigeon pancreas slices. Phosphatidic acid is the first phosphatide to show increased 32P incorporation in response to hormone. The kinetics of 32P uptake indicate that a fraction of phosphatidic acid is formed which undergoes continuous turnover. The kinetics of 32P incorporation into phosphatidylinositol are compatible with the interpretation that the fraction of phosphatidic acid which is formed is a pool of intermediate for the synthesis of phosphatidylinositol in response to hormone in the pancreas. The fraction of phosphatidic acid which is formed in response to hormone disappears on removal of the hormone and appears to be converted to phosphatidylinositol. A new fraction of phosphatidic acid is formed if the tissue is again exposed to hormone. The experimental data are interpreted as indicating that the point of action of pancreozymin and acetylcholine on this aspect of phosphatide metabolism in the pancreas may involve activation of diglyceride kinase.