Involvement of ovarian steroids in basal and oxytocin-stimulated prostaglandin (PG) F2 alpha secretion by the bovine endometrium in vitro

It is assumed that exposure of endometrium to spontaneously secreted luteal hormones stimulates PGF2 alpha secretion and modifies oxytocin (OT) influe nce on the bovine uterus. At first, the time-dependent effect of endogenous luteal products on endometrial PGF2a secretion was examined. Endometrial s trips (100 mg) from slaughtered heifers (Days 11 to 17 of the cycle) were i ncubated alone or with luteal cells (1x10(5) cells/mL). The highest PGF2a s ecretion by the endometrium under influence of hormones secreted from lutea l cells was observed after 12 h of incubation compared with the control (P< 0.001). Then, endometrium (Days 11 to 17) was incubated with luteal cells a nd concomitantly with antagonists of P4 and OT. The P4 antagonist prevented the stimulatory effect of endogenous luteal hormones on PGF2a secretion (P <0.05), but the OT antagonist did not. Further, direct effects of exogenous P4, OT and estradiol (E2) on endometrial PGF2a secretion (Days 11 to 17) w ere examined. Both OT and Ps increased PGF2a secretion (P<0.05); E2 alone h ad no effect on PGF2a secretion, but it amplified the P4 effect (P<0.05). F inally, we studied the effect of endogenous luteal products on OT-stimulate d PGF2a secretion from endometrium. When endometrium (Days 11 to 17) was in cubated without luteal cells, OT stimulated PGF2a secretion (P<0.001), wher eas incubation of endometrium with luteal cells abolished the stimulatory e ffect of OT on PGF2a secretion (P<0.001). These treatments did not affect P GF2a. secretion from the endometrium collected on Days 1 to 4. In conclusio n, P4 stimulates PGF2a secretion by the endometrium and E2 amplifies this e ffect. As long as the endometrium is under the influence of P4, ovarian OT does not affect PGF2a secretion. (C) 1999 by Elsevier Science Inc.