Effect of luteinizing hormone (LH), pregnancy specific protein B (PSPB), or arachidonic acid (AA) on ovine endometrium of the estrous cycle or placental secretion of prostaglandins E2 (PGE2) and F2alpha (PGF2alpha) and progesterone in vitro.

The objective of this experiment was to determine the effect of AA, LH, or PSPB on secretion of PGE2, PGF2alpha, or progesterone by ovine caruncular endometrium of the estrous cycle or placental tissue of pregnancy in vitro. Ovine caruncular endometrium of the estrous cycle (days 8, 11, 13, and 15) or caruncular/placental tissue on days 8, 11, 13, 15, 20, 30, 40, 50, 60, and 90 postbreeding were incubated in vitro with vehicle, AA, LH, or PSPB in M-199 for 4 and 8 h. Secretion of PGF2alpha by caruncular endometrium of non-bred ewes on days 13 and 15 and by caruncular/placental tissue of bred ewes on days 13, 15, 20, 30, and 40 was increased (P < or = 0.05) when incubated with vehicle and declined (P < or = 0.05) after day-40 in bred ewes. Secretion of PGF2alpha by day-15 caruncular endometrium of non-bred ewes and bred ewes was increased (P < or = 0.05) by AA on days 13 and 15 and by LH on day-15. Secretion of PGF2alpha by caruncular/placental tissue from bred ewes was (P < or = 0.05) by AA on days 13, 15, 20, 30, and 40 and by LH on days 15, 20, 30, and 40, after which the response decreased (P < or = 0.05). Secretion of PGF2alpha by caruncular endometrium of non-bred ewes during the estrous cycle or by caruncular/placental tissue of bred ewes during the first trimester was not affected by PSPB (P > or = 0.05). Secretion of PGE2 by caruncular endometrium of non-bred ewes did not change (P > or = 0.05) and was increased (P < or = 0.05) by caruncular/placental tissue on days 13-90 from bred ewes when incubated with vehicle. Secretion of PGE2 by endometrium from non-bred ewes was not affected (P > or = 0.05) by AA, LH, or PSPB, but was increased (P < or = 0.05) by AA or LH on days 13-50 and by PSPB on days 60 and 90 when incubated with caruncular/placental tissue from bred ewes. Secretion of progesterone by placental tissue of bred ewes increased (P < or = 0.05) on day-50 and continued to increase through day-90. In summary, uterine/placental tissue secretion of PGF2alpha is not reduced until the end of the first trimester of pregnancy in ewes. In addition, LH appears to play a role in luteolysis of non-bred ewes by stimulating caruncular endometrial secretion of PGF2alpha and on day-5 postbreeding to prevent luteolysis during early pregnancy by stimulating caruncular/placental secretion of PGE2 throughout the first trimester of pregnancy in sheep. Secretion of PGE2 by caruncular/placental tissue after day-50 of pregnancy appears to be regulated by PSPB, not LH.