PROPOSED SIGNALING ROLE OF ARACHIDONIC-ACID IN HUMAN MYOMETRIUM

The objective of this study was to test the hypothesis that, in human myometrial cells (HMC), PGF(2 alpha) and oxytocin promote the release of arachidonic acid (AA) which, in turn, acts to mobilize intracellula r Ca2+. Primary monolayer cultures of HMC were labeled with [H-3]arach idonic acid ([H-3]AA) to isotopic equilibrium before exposure to PGF(2 alpha) or oxytocin. Radiolabeled phospholipids were separated on thin layer chromatography and quantitated by scintillation counting. Prost anoids were analyzed by high performance liquid chromatography. Calciu m release was quantitated in digitonin-permeabilized myocytes preloade d with Ca-45, in the presence of ATP and ruthenium red. PGF(2 alpha) ( 10(-7) M) caused a rapid (peaking at 2 min), and significant (P < 0.01 ) increase in [H-3]AA release that was derived selectively from phosph atidylethanolamine (PE), indicative of phospholipase Aa activation. Ox ytocin caused a rapid (30 s) and significant increase in diacylglycero l, concomitant with a drop in phosphoinositides, as well as an increas e in [H-3]AA and a fall in PE and phosphatidylcholine. Exogenous AA ca used a rapid and dose-related efflux of Ca-45(2+), which was not inhib ited by blockers of AA metabolism, or by heparin that abolished inosit ol 1,4,5-trisphosphate-induced Ca-45(2+) release. It is concluded that PGF(2 alpha) and oxytocin promote, by different mechanisms, the relea se of AA, which in turn may amplify their action by enhancing Ca2+ mob ilization from the sarcoplasmic reticulum, thereby fulfilling the role of intracellular signaling molecule in human myometrium.