CONICET | Buscador de Institutos y Recursos Humanos

INTRODUCTION: Maternal recognition of pregnancy (MRP) is considered as the interaction between the maternal unit and products of conception whereby the conceptus signals its presence to the maternal system and prolongs lifespan of the corpus luteum. In llamas, it has been proposed that MRP should occur between days 8 to 12 post mating (Aba et al., 2000), however there is no information regarding the molecular changes that occur in the endometrium during this period. The aim of the present study was to compare the population of estrogen receptor α (ERα) and progesterone receptor (PR) and cyclooxygenase-2 (COX-2) expression in the luminal (LE) and glandular (GE) epithelium and stroma (Str) of the endometrium of non pregnant llamas versus pregnant animals. MATERIALS AND METHODS: Females (n = 23) were divided into two groups: non pregnant llamas (n =5) were induced to ovulate with a GnRH injection. In these animals, endometrial samples were obtained throughout transcervical biopsy on day 8 or day 12 post induction of ovulation. Animals of the Pregnant group (n = 18) were mated with a fertile male. Pregnancy was confirmed by the visualization of the embryo collected by transcervical flushed in 5/9 animals on day 8 post mating and by progesterone profile on day 12 post mating in 4/9 animals. Animals with plasma progesterone concentrations above 1 ng ml-1 on day 12 post mating were considered pregnant (Sumar, 1996). An immunohistochemical technique (avidin-biotin peroxidase) was used to evaluate receptors population and COX-2 expression. Both receptors and COX-2 expression was evaluated as percentage of positive area in the LE, GE and Str and analyzed by the mixed procedure of SAS. RESULTS: Both receptors staining was visualized in the three cell types. Conversely, COX-2 was never expressed in the Str. The most significant changes were recorded in the LE. An increased of positive cells to ERα was observed on days 8 and 12 post mating in the endometrium of pregnant animals. Meanwhile, a lesser expression of PR and COX-2 was reported on day 12 post induction of ovulation in pregnant versus non pregnant llamas (see table). Estrogen receptor α Day 8 Non preg Day 8 Pregnant Day 12 Non pre Day 12 Preg. LE 91,90 ± 0,7a 98,60 ± 0,3b 80,38 ± 2,8a 92,00 ± 1,6b GE 98,00 ± 0,7b 99,00 ± 1,8b 95,60 ± 0,7b 96,17 ± 0,6b Str 34,90 ± 2,3c 51,10 ± 0,8d 38,50 ± 1,9c 27,08 ± 4,0d Progesterone receptor LE 73,36 ± 0,9a 82,17 ± 2,8a 37,50 ± 4,9b 4,88 ± 2,4c GE 95,40 ± 1,6a 99,00 ± 0,3a 91,69 ± 2,3a 74,50 ± 3,6a Str 25,71 ± 3,6b 34,64 ± 3,1b 28,19 ± 2,0b 14,75 ± 2,6c Cyclooxygenase-2 LE 73,00 ± 7,4a 70,00 ± 9,8ª 93,70 ± 3,4a 34,20 ± 11,8b GE 34,00 ± 13,9b 52,00 ± 8,3b 42,90 ± 12,0b 43,20 ± 14,5b Data are expressed as percentages of positive area ± SEM. Different letters indicate significant statistical differences. DISCUSSION AND CONCLUSION: The increase of ERα expression on days 8 and 12 post mating gives further support to the hypothesis that estrogens could be involved in the signaling of MRP in camelids (Powell et al., 2007). The loss of PR in the epithelia during MRP is similar to what is observed in other species and it seems to be essential for the induction of proteins necessary for embryo implantation (Spencer and Bazer, 2004). In addition, the decrease of COX-2 expression at day 12 post mating in the LE of pregnant llamas could be responsible for the reduction of PGF2α secretion during the MRP. Thus, it seems that the embryo throughout the release of estrogens would induce a decrease in the expression of COX-2 and consequently, would inhibit the process of luteolysis. Aba, MA y col. (2000). Anim Reprod Sci. 50, 111-121. Spencer, TE y Bazer, FW (2004) Reprod. Biol. and Endocrinol. 2, 49. Powell, SA y col. (2007) Anim Reprod Sci. 102, 66-75. Sumar, J (1996) Anim Reprod Sci 42, 405-415.