Research articleEffects of periovulatory gonadotrophin treatment on luteal function and endometrial expression of selected genes in cyclic pony mares

Progestin concentration in plasma during the early luteal phase is crucial for endometrial function and conceptus development. We hypothesized that periovulatory gonadotrophin treatment via support of luteal function affects endometrial gene expression in horses. Effect of age was analyzed as well. Shetland mares (n = 8, age 4-25 years) were assigned to the following treatments during five consecutive cycles in alternating order following a cross-over design: treatment hCG/-: preovulatory injection of hCG, but no gonadotrophin injection at detection of ovulation, treatment -/hCG: no preovulatory gonadodrophin injection, but injection of hCG at detection of ovulation, treatment eCG/-: preovulatory injection of eCG, but no gonadotrophin injection at detection of ovulation, treatment -/eCG: no preovulatory gonadotrophin injection, but injection of eCG at detection of ovulation, treatment control: no treatment. Concentration of progestin was analyzed by ELISA from the day of ovulation until Day 10. On Day 10, endometrial cells were collected transvaginally by cytobrush technique. Expression of mRNA of cyclooxygenase-2 (COX-2), prostaglandin F2α-synthase, prostaglandin E-synthase, progesterone receptor (PR), estradiol receptor (E2R), acyl-CoA-dehydrogenase (ACAD), uteroglobin (UGB), uteroferrin, and uterocalin was analyzed by RT qPCR. Immunohistological staining of endometrial tissue, obtained via biopsy, was performed for COX-2, PR and UGB. The P4 concentration was influenced by day of cycle (P < 0.01), but not by treatment. No effects of age on gene expression were determined. Neither of the periovulatory gonadotrophin treatments nor age influenced mRNA expression of the genes of interest. Treatment did also not affect immunohistological staining of the endometrium. In contrast, age affected the percentage of PR positive stromal cells (e.g. mare 1 (4 years): 65.5 ± 2.6, mare 2 (24 years): 82.7 ± 2.2%, P < 0.05) and COX-2 positive stained ciliated cells (e.g. mare 1: 15.8 ± 2.9, mare 2: 33.4 ± 6.0%, P < 0.05). In conclusion, no effects of periovulatory gonadotrophin treatment and age on endometrial gene expression in luteal phase pony mares were reported. A lack of treatment effects on luteal function and expression of PRs in the endometrium can at least in part be explained by differences in the reproductive physiology between horses and ponies.