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

Abstract

The induction of endometrial prostaglandin (PG) F 2α synthesis by oxytocin is dependent upon activation of phospholipase (PL) A 2 and mobilization of arachidonic acid. The objective of this study was to determine if oxytocin stimulates PGF 2α synthesis by inducing synthesis of cytosolic PLA 2 (cPLA 2). In Experiment 1, 15 ovariectomized ewes were given progesterone and estradiol to simulate an estrous cycle. Ewes were then given an injection of oxytocin on Day 14 of the simulated estrous cycle. Jugular blood samples were collected and assayed for 13,14-dihydro-15-keto-prostaglandin F 2α (PGFM). Uteri were collected at 0, 7.5, 25, 90, or 240 min postinjection (n = 3 ewes/time point). Total RNA was isolated from caruncular endometrium and subjected to dot-blot analysis. Oxytocin induced a rapid and transient increase in serum PGFM (P < 0.01). However, endometrial concentrations of cPLA2 mRNA did not change following oxytocin administration (P > 0.10). In Experiment 2, 11 ovary-intact ewes were given oxytocin (n = 5) or saline (n = 6) on Day 15 after estrus. Jugular blood samples were collected and assayed for serum concentrations of PGFM. Uteri were collected at 15 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 postinjection (P < 0.01). Endometrial concentrations of cPLA 2 protein were greater 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 protein in ovine endometrium. Oxytocin may stimulate PGF 2α synthesis by activating cPLA 2 protein that is already present in an inactive form.