Endometrial expression of estrogen and progesterone receptors in non-cyclic mares treated only with long-acting progesterone

Abstract

Administration of progesterone (P4) after estradiol is usually performed to prepare non-cyclic mares as embryo recipients. However, there are successful pregnancy reports after embryo transfer in non-cyclic mares treated only with progestins. The objective of this study was to evaluate endometrial gene expression and immunostaining for estrogen receptor alpha (ERα), beta (ERβ) and progesterone receptor (PR) in seasonal anestrous mares treated with long acting P4 (LA P4). Endometrial tissue from eight seasonal anestrous mares was collected immediately before administration of 1.5 g of LA P4 and five days after. The receptors protein expression was evaluated by immunohistochemistry and the percentage of the immunostained area was determined by ImageJ software. Transcripts abundance for ERα, ERβ and PR were determined by RT-qPCR. Blood samples were collected daily to measure plasma P4 concentrations. Protein expression for ERα was greater (p < 0.05) after LA P4 administration, although gene expression was not affected by treatment (p > 0.05). There was no difference for ERβ protein expression (p = 0.07) and ERβ gene expression was reduced (p < 0.05) after treatment. Gene and protein expression for PR was not altered (p > 0.05). In conclusion, endometrial PR and ERα expression patterns after LA P4 administration were similar to those previously found in protocols using estradiol prior to LA P4 to prepare non-cyclic mares as embryo recipients.

The Timing of the Maternal Recognition of Pregnancy Is Specific to Individual Mares

“…A side issue to note here is that in an early pregnant animal PGR in the uterine stromal glands remain expressed and when progesterone binds to them, it triggers the production of progestamedins that aid conceptus development and the secretion of histotroph from endometrial glands [44]. In mares, the sequential and spatial expression of PGR in the endometrium of cyclic and early pregnant mares has been examined using various techniques [45][46][47][48][49][50] which demonstrated that both mRNA and localisation of PGR decline to a nadir in late dioestrus.…”