173. Intraluteal Prostaglandin Biosynthesis and Signaling Are Selectively Directed Towards PGF2a During Luteolysis and Towards PGE2 During the Establishment of Pregnancy in Sheep. (2012)

INTRODUCTION: In ruminants, pulsatile endometrial PGF2a secretion causes functional luteolysis while secondary stimulation of intraluteal PGF2a synthesis is thought to cause structural luteolysis. In early pregnancy, intraluteal biosynthesis of PGE2 is considered to play a luteoprotective role and thus helps to maintain pregnancy. The regulation of intraluteal biosynthesis and signaling of PGF2a and PGE2 during the cycle and in early pregnancy are incompletely understood. Trophoblast interferon tau (INFT), which reduces endometrial PGF2a synthesis in early pregnancy, is proposed to exert a luteoprotective effect on the CL at this time. OBJECTIVES: 1) Compare the intraluteal production of PGF2a and PGE2 on days 12, 14, and 16 of the cycle or pregnancy; 2) determine proteins involved in intraluteal PGF2a and PGE2 biosynthesis, signaling, catabolism, and transport during days 12, 14, and 16 of the cycle or pregnancy; 3) investigate transport through the vascular utero-ovarian plexus (UOP) of PGF2a, PGE2, and INFT from the uterus to ovary during pregnancy. METHODS: Ewes were bred with either intact or vasectomized rams on days 12, 14, and 16 of the cycle (n=4 ewes/day). On each of these days, a laparotomy was performed under fluothane/O2. Blood samples (5ml) were collected from the utero-ovarian vein, the ovarian vein, and the ovarian artery ipsilateral to the CL. Ovariohysterectomy was then performed and uterine flushings (UF) and sections of the uterine horns and CLs were collected. Portions of CL tissue were also used for luteal explant culture. Tissues were processed for immunohistochemistry as well as for protein measurement. Western blots were used to determine luteal protein levels of COX-1, COX-2, PGES-1, PGES-2, PGES-3, AKR1B1-PGFS, AKR1C3-PGFS, PGDH, FP, EP1, EP2, EP3, EP4, or PGT. ELISA was used to measure the concentration of PGF2a and PGE2 in luteal tissue and in media from CL explant cultures. The level of INFT in UF, luteal tissue, utero-ovarian venous plasma, and ovarian arterial plasma, was determined by ELISA and/or Western blot analysis. RESULTS: We found that: 1. Intraluteal biosynthesis and signaling is selectively directed towards PGF2a over the time of luteolysis and towards PGE2 during the establishment of pregnancy. 2. The resistance of the CL of early pregnancy to PGF2a is due to increased intraluteal biosynthesis of PGE2 and EP2 and EP4 mediated PGE2 signaling. 3. During early pregnancy, INFT is not secreted by the uterus into the utero-ovarian vein nor transported to the CL via the vascular UOP but a large proportion of endometrial PGE2 in early pregnancy is transported from the uterus to the CL via this vascular pathway. CONCLUSIONS: We conclude that endometrial PGE2 induced by pregnancy is transported locally to the CL where it induces luteal PGE2 biosynthesis and activates EP2 and EP4 signaling thus protecting the CL during the establishment of pregnancy in sheep. We also find no evidence of a role for trophoblast INFT in locally or systemically protecting the CL during the establishment of pregnancy in this species. (Supported by USDA NIFA Competitive Grant #2008-35203 awarded to JAA and in part by USDA NIFA Competitive Grant #2004-3520-14176 awarded to JAMcC