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1Human Reproduction Unit, Department of Physiology, University of Sydney, Royal North Shore Hospital of Sydney, St. Leonards, New South Wales 2065; and 2Faculty of Veterinary Science, University of Sydney, Sydney, New South Wales 2006, Australia
Submitted 11 July 2003 ; accepted in final form 10 February 2004
Pulsatile release of uterine prostaglandin F2
(PGF2
) induces luteolysis in ruminants. Exogenous PAF is well known to cause PGF2
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 PGF2
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 PGF2
pulsatility was first observed.
endometrium; luteolysis; platelet-activating factor; prostaglandin F2
; PAF:acetylhydrolase (EC 3.1.1.47)
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