EFFECTS OF PROGESTERONE AND ESTRADIOL ON PROSTAGLANDIN ENDOPEROXIDE SYNTHASE IN OVINE ENDOMETRIAL TISSUE

In experiment 1, 20 ovariectomized ewes were used to determine how pro gesterone and estradiol interact to regulate endometrial concentration and activity of prostaglandin endoperoxide synthase (PGS). Ewes were randomly assigned to one of four treatment groups: (I) control (n = 5) ; (2) estradiol (n = 5); (3) progesterone (n = 5); (4) progesterone an d estradiol (n = 5). Groups 3 and 4 received twice daily injections of progesterone for 15 days, The dose of progesterone was varied to simu late concentrations of progesterone observed in intact ewes during the estrous cycle. Estradiol was administered to groups 2 and 4 by subcut aneous silastic implants which maintained circulating concentrations o f estradiol of approximately 3 pg ml(-1). Ewes were slaughtered on day 16, A portion of uterine tissue was fixed and stained, immunohistoche mically, for PGS. Treatment with progesterone induced an increase in e pithelial cell height (P < 0.01) and an increase in intensity of stain ing for PGS in epithelial cells (P < 0.01), Explants of caruncular end ometrial tissue were collected from each ewe and incubated in the pres ence or absence of arachidonic acid (20 mu g ml(-1)) to quantify relea se of PGF(2 alpha), in vitro, Release of PGF(2 alpha) in the presence of arachidonic acid was used as a functional assessment of PGS activit y. Release was greater for tissue collected from groups treated with p rogesterone (P < 0.01). Within progesterone treated groups, release wa s greater, for tissue from ewes that also received estradiol (P < 0.05 ), Release of PGF(2 alpha) was enhanced by the addition of arachidonic acid (P < 0.01). Maximal release of PGF(2 alpha) in the presence of a rachidonic acid was observed in tissue from ewes receiving progesteron e and estradiol. In experiment 2, 19 ewes were randomly assigned to on e of four treatment groups: (1) control (n = 4); (2) estradiol (n = 5) ; (3) progesterone (n = 5); (4) progesterone and estradiol (n = 5), St eroids were administered as in experiment 1 with minor modification in doses of progesterone. Uteri were collected on day 16. Explants of ca runcular endometrial tissue were incubated in the presence of one of f our treatments: (1) no additions; (2) arachidonic acid (20 mu g ml(-1) ); (3) oxytocin (10(-6) M); (4) arachidonic acid and oxytocin. The eff ects of ovarian steroids on release of PGF(2 alpha) from caruncular en dometrial explants were similar to those described in experiment 1. Bo th arachidonic acid and oxytocin increased release of PGF(2 alpha) (P < 0.01, P < 0.01, respectively). However, release of PGF(2 alpha) was not enhanced by arachidonic acid when administered in the presence of oxytocin. We conclude that the ability of ovarian steroids to regulate endometrial secretion of PGF(2 alpha) may be exerted, in part, throug h their ability to regulate the concentration and activity of PGS.