Abstract
Simple SummaryWhile intrauterine devices (IUDs) are used to prevent disturbing oestrous behaviour in sport mares, their mechanism of action has not been elucidated. The presence of an embryo or an IUD prevents cyclooxygenase-2 (COX-2) and subsequently prostaglandin (PG) release and luteolysis. It has been suggested that a plastic sphere would mimic the embryo by mechanotransduction. However, there is some evidence that IUDs also cause endometrial inflammation, which might contribute to luteostasis. The aim of this study was to investigate the presence and time course of possible inflammation by evaluating changes in uterine fluid composition. On Day 10 after ovulation, events leading to COX-2 and prostaglandin F2α (PGF2α) inhibition start, whereas either luteolysis occurs or the corpus luteum is maintained on Day 15. Therefore, uterine lavage fluid was evaluated at two time points in inseminated mares, either pregnant or not, and in mares inserted with an IUD. On Day 10, PGF2α concentration in the fluid was significantly lower in the IUD group than in the pregnant mare one but did not differ from the non-pregnant mare group. On Day 15, the IUD group had significantly higher levels of the modulatory cytokine IL-10 and inhibin A, which could indicate previous inflammation and resolution stage.Intrauterine devices (IUDs) are used in mares to suppress oestrous behaviour, but the underlying mechanism is yet to be elucidated. The presence of an embryo or an IUD prevents cyclooxygenase-2 (COX-2) and, subsequently, prostaglandin (PG) release and luteolysis. However, inflammation may also be involved. Endometrial inflammatory markers in uterine lavage fluid were measured on Day 10 (EXP 1, n = 25) and Day 15 (EXP 2, n = 27) after ovulation in inseminated mares, non-pregnant or pregnant, and in mares in which a small plastic sphere had been inserted into the uterus 4 (EXP 1) or 3 days (EXP 2) after ovulation. Uterine lavage fluid samples were analysed for nitric oxide (NO), prostaglandin E2 (PGE2) (only EXP 1), prostaglandin F2α (PGF2α), inhibin A and cytokines, and blood samples for progesterone and oestradiol. On Day 10, the concentration of PGF2α was lower (p < 0.05) in the IUD group than in pregnant mares. The concentration of the modulatory cytokine IL-10 was significantly higher in the IUD group in comparison to non-pregnant mares, and inhibin A was significantly higher in IUD mares than in the pregnant counterparts on Day 15. The results suggest that the presence of IUD causes endometrial inflammation which is at a resolution stage on Day 15.
Highlights
Intrauterine devices (IUDs) are used in sports mares to prevent unwanted oestrous behaviour [1]
Small numbers of bacteria were cultured from the lavage fluid of two mares, but they were not associated with endometritis since all the smears were negative for polymorphonuclear leukocytes (PMN), and no uterine fluid or oedema was visible on the ultrasonography
On Days 10 and 15, the IUD had been in the uterus for six and twelve days, respectively, and the possible inflammation would be of chronic nature at that time
Summary
Intrauterine devices (IUDs) are used in sports mares to prevent unwanted oestrous behaviour [1]. Their efficacy, is highly variable; prolonged luteal phases have been reported in 0% to 75% of mares or cycles [1,2,3]. F2α (PGF2α ) is released from the endometrium as several spikes between Days 14 to 17 of the cycle resulting in luteolysis [4]. Both the embryo and IUD prevent PGF2α release by inhibiting cyclooxygenase-2 (COX-2) [5,6] and, as a consequence, prevent luteolysis. Direct contact of the embryo with the endometrium, enhanced by actively moving around in the uterus, is probably important in the inhibition of luteolysis by attenuating the secretion of PGF2α [7]
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