Effect of oxytocin on expression of cytosolic phospholipase A(2) mRNA and protein in ovine endometrial tissue in vivo

The induction of endometrial prostaglandin (PG) F-2 alpha synthesis by oxyt ocin is dependent upon activation of phospholipase (PL) A(2) and mobilizati on of arachidonic acid. The objective of this study was to determine if oxy tocin stimulates PGF(2 alpha) synthesis by inducing synthesis of cytosolic PLA(2) (cPLA(2)). In Experiment 1, 15 ovariectomized ewes were given proges terone and estradiol to simulate an estrous cycle. Ewes were then given an injection of oxytocin on Day 14 of the simulated estrous cycle. Jugular blo od samples were collected and assayed for 13,14-dihydro-15-keto-prostagland in F-2 alpha (PGFM). Uteri were collected at 0, 7.5, 25, 90, or 240 min pos tinjection (n = 3 ewes/time point). Total RNA was isolated from caruncular endometrium and subjected to dot-blot analysis. Oxytocin induced a rapid an d transient increase in serum PGFM (P < 0.01). However, endometrial concent rations of cPLA2 mRNA did not change following oxytocin administration (P > 0.10). In Experiment 2, 11 ovary-intact ewes were given oxytocin (n = 5) o r saline (n = 6) on Day 15 after estrus. Jugular blood samples were collect ed acid assayed for serum concentrations of PGFM. Uteri were collected at 1 5 min postinjection. Homogenates were prepared from caruncular endometrium and subjected to Western blot analysis. Concentrations of PGFM were higher in oxytocin treated ewes compared to saline treated ewes at 15 min postinje ction (P < 0.01). Endometrial concentrations of cPLA(2) protein were greate r in the cytosolic than in the microsomal fraction (P < 0.01). Oxytocin did not affect the amount of cPLA(2) protein in either fraction (P > 0.10). In conclusion, oxytocin did not effect expression of either cPLA(2) mRNA or p rotein in ovine endometrium. Oxytocin may stimulate PGF(2 alpha) synthesis by activating cPLA(2) protein that is already present in an inactive form. (C) 2000 Elsevier Science Inc. All rights reserved.