The involvement of phospholipase A₂ in ethanol-induced gastric muscle contraction

To understand the underlying mechanism of ethanol in tonic contraction, the effect of ethanol on phospholipase A₂ and phospholipase C activities and the effects of phospholipase inhibitors on ethanol-induced contraction of cat gastric smooth muscle were tested. Circular muscle strips (2.0 × 0.2 cm) obtained from the fundus of cat stomach were used to measure isometric contraction. Ethanol elicited tonic contraction and activated phospholipase A₂ activity in a dose-dependent manner. Phospholipase A₂ inhibitors, manoalide (0.1-10 μM) and oleyloxyethyl phosphorylcholine (1-10 μM), significantly inhibited ethanol-induced contraction. Furthermore, 342 mM ethanol-induced contraction was significantly inhibited by cyclooxygenase inhibitors, ibuprofen (10-100 μM) and indomethacin (10-100 μM), but not by lipoxygenase inhibitors. On the other hand, phospholipase C inhibitors had no effect on ethanol-induced contraction, indicating that phospholipase C is not involved in ethanol-induced contraction. It is suggested from the above results that ethanol-induced contraction in cat gastric smooth muscle is, in part, mediated by phospholipase A₂ and cyclooxygenase pathways.