Components of a platelet-activating factor-signaling loop are assembled in the ovine endometrium late in the estrous cycle

Abstract

Pulsatile release of uterine prostaglandin F2α (PGF2α) induces luteolysis in ruminants. Exogenous PAF is well known to cause PGF2α release from the ovine uterus. This study examines whether the components of a PAF-signaling loop exist in sheep at the time luteolysis is normally initiated. Day 14 of the cycle was the first day the uterus responded to an infusion of PAF, inducing a significant short-term increase in circulating levels of the PGF2α metabolite. There was a significant increase of PAF concentration ( P < 0.001) in the endometrium and PAF release by tissue explants ( P < 0.001) from day 10 to day 16 of the cycle. Endometrial tissue PAF receptor mRNA expression was induced ( P < 0.01) by estradiol and progesterone treatment of animals, and transcripts were present between days 10 and 16 of the estrous cycle. Western analysis of endometrial tissue showed marked upregulation of PAF receptor protein expression from day 14 of the cycle, and immunolocalization studies showed that the receptor expression was predominantly around the endometrial glands. PAF:acetylhydrolase was primarily located within the lumen of the endometrial glands. The study shows that a PAF-signaling loop was assembled within the ovine endometrium at the time that PGF2α pulsatility was first observed.

The Role of Platelet‐activating Factor in the Mammalian Female Reproductive Tract

“…Thus, even if relatively constant levels of PAF production occur in the uterus, pulsatile release of PGF2α may occur because of the periodicity of responsiveness of the uterus to PAF. This PAF induced luteolysis hypothesis was confirmed by results published by Chami et al (2004). These authors indicated that the uterus in ewe responded to an infusion of PAF on day 14 of the cycle by increasing the circulating levels of the inactive PGF2α metabolite (PGFM).…”

“…(1998) reported that PAF‐R immunoreactivity and mRNA were predominantly detected in human endometrial tissue from the proliferative phase of the menstrual cycle. In ewes, endometrial tissue PAF‐R mRNA expression was significantly induced by estradiol and progesterone in vivo treatment and transcripts were presented between days 10 and 16 of the oestrous cycle (Chami et al 2004). After ovariectomy, PAF concentration in the uterus of rats significantly declined, and this could be restored by treatment with estradiol (Nakayama et al 1991).…”

“…An explanation could be given by the data reported by Chami et al (1999), who found that the ovine uterus only responds to PAF if it is oestrogen‐ and/or progesterone‐primed in vivo . Significant increase of PAF concentration was found in the endometrium of ovine on days 10–16 of the cycle (Chami et al 2004). These authors observed a PAF release by endometrial explants derived from ovine at cyclic days 10 and 16.…”

Expression of platelet activating factors and its receptor in cat uterus during early pregnancy

“…The PAF and PAF-R (receptor) synthesis is affected by the presence of steroids in the endometrium in humans (42). Endometrial PAF-R mRNA expression was significantly induced by estradiol and progesterone in sheep (11). After ovariectomy, concentration of PAF in the rat uterus was declined (25).…”