Estrogen and Progesterone Receptors and COX-2 Expression in Endometrial Biopsy Samples During Maternal Recognition of Pregnancy in Llamas (Lama glama)

Abstract

Endometrial expression of oestrogen receptor-a (ERa),progesterone receptor (PR) and cyclooxigenase-2 (COX-2)was evaluated in non-pregnant and pregnant llamas during theperiod when luteolysis/maternal recognition of pregnancy isexpected to occur. Females (n = 28) were divided into twogroups: non-pregnant llamas were induced to ovulate with aBuserelin injection, and endometrial biopsies were obtained onday 8 (n = 5) or 12 (n = 5) post-induction of ovulation.Animals of the pregnant group (n = 18) were mated with afertile male. Pregnancy was confirmed by the visualization ofthe embryo collected by transcervical flushing in 5 of 9 animalson day 8 post-mating and by progesterone profile on day 12post-mating in 4 of 9 animals, when endometrial biopsies wereobtained. An immunohistochemical technique was used toevaluate receptors population and COX-2 expression.Pregnant llamas showed a higher percentage of positive cellsand stronger intensity for ERa than for non-pregnant llamasin stroma on day 8 and in the luminal epithelium on day 12post-induction of ovulation, while a deep decrease in endometrialPR population was reported in pregnant llamas on thatday in luminal and glandular epithelia and stroma. In theluminal epithelium, COX-2 expression was lower in pregnantthan in non-pregnant animals. Briefly, the increase of ERa inpregnant llamas gives further support to the hypothesis thatoestrogens are involved in the mechanism of maternal recognitionof pregnancy. Endometrial PR decrease in pregnantllamas might be a necessary event to allow the expression ofproteins involved in conceptus attachment, a mechanismwidely accepted in other species. Moreover, embryo seems toattenuate maternal PGF2a secretion during early pregnancy bydecreasing the endometrial expression of COX-2 in the luminalepithelium of pregnant llamas.