Evidence for a role in stimulus--secretion coupling of prostaglandins derived from release of arachidonoyl residues as a result of phosphatidylinositol breakdown

Abstract

That stimulation of secretion in exocrine and endocrine glands is associated with increased turnover of phosphatidylinositol and phosphatidic acid has been known for many years. In the present work, mouse pancreases were prelabeled with [14C]arachidonic acid in the presence of the secretogogue carbamoylcholine. They were then incubated in media containing atropine and 1% albumin. The atropine causes the tissue to revert to the resting state, and the albumin binds free [14C]arachidonic acid. The tissues were finally incubated in media containing no stimulant or the stimulant caerulein, which is not blocked by atropine. Stimulation with caerulein, which is not blocked by atropine. Stimulation with caerulein led to a 44% loss of [1-14C]arachidonic acid from phosphatidylinositol. About half of this released arachidonic acid ended up in phosphatidic acid. The remainder of the loss could not be accounted for in any other lipid. No other phospholipids showed statistically significant changes on stimulation. Several lines of evidence indicated that the missing arachidonic acid was converted to prostaglandins, which play a role in stimulus--secretion coupling. Four nonsteroidal anti-inflammatory drugs inhibited secretogogue-induced amylase secretion from pancreases, and their potencies paralleled their potencies in inhibiting cyclooxygenase, which converts arachidonic acid to prostaglandins. Amylase secretion was stimulated by arachidonic acid, and this stimulation was blocked by the nonsteroidal anti-inflammatory drug indomethacin. Other fatty acids failed to elicit amylase secretion. At concentrations of 3--10 nM, prostaglandins I2, E1, E2, D2, and F2 alpha gave statistically significant stimulations of secretion. Other prostaglandins tested gave no significant stimulation.