Altered gene expression in embryos and endometrium collected on day 8 of induced aluteal cycles in mares.

Aluteal cycles were induced in the mare to evaluate the effects of progesterone deprivation on the gene expression of embryos and endometrium collected eight days after ovulation. We hypothesized that the transcript expression would be altered during induced aluteal (AL) cycles (low progesterone <1 ng/mL) when compared with control cycles during diestrus (high progesterone; > 4 ng/mL) for 1) the embryonic expression of progesterone-mediated transcripts and those related to normal embryo growth and development and 2) the endometrial expression of progesterone-mediated transcripts and those related to prostaglandin synthesis and normal pregnancy establishment. Seven cyclic mares with a median age of 6.5 years (range 3-16) were utilized in a crossover design. Mares in estrus were artificially inseminated to a fertile stallion and randomly assigned to control or AL groups. Mares received either saline solution (control mares) or PGF2α (AL mares), twice daily on days 0, 1, and 2 and once daily on days 3 and 4. Serial blood samples were collected daily from day 0 (ovulation) until the day of embryo collection and endometrial biopsy on day 8. Mares were monitored until they returned to estrus, and artificially inseminated. Mares were switched to the opposite treatment group only after a successful embryo collection occurred during the previous cycle and only cycles that produced embryos were used for analyses. The study design resulted in paired samples from each mare for analyses. No significant rise in progesterone was observed in the AL group with mean concentrations of plasma progesterone remaining <1.0 ng/mL from ovulation until embryo collection on day 8. This is in sharp contrast to the control (luteal) cycle where a post-ovulatory rise in plasma progesterone was observed. Real-time RT-PCR was utilized to evaluate the expression of ESR1, PGR, CYP19A1, P19, SLC35A1, OCD, APOB, AQP3, NEU2 transcripts in the embryos and PTGS2, P19, ESR1, HK2, sPLA2, PGR, CTGF, IFNE, FGF9, SLC36A2 expression in the endometrium. Four transcripts showed increased expressed in embryos developed during AL cycles ESR1, P19, APOB and PGR (p < 0.05). Four transcripts showed increased expressed in endometrium developed during AL cycles sPLA2, PGR, ESR1, FGF9 (p < 0.05) and four transcripts showed decreased expression P19, CTGF, IFNE, HK2 (p < 0.05). Additionally, staining differences were present in endometrial staining for both ERα and PR receptor during AL cycles compared with control cycles. Embryos and endometrium developed in a progesterone-deprived environment during induced aluteal cycles demonstrated altered transcript expression. These results indicate that adequate progesterone levels may be a key mediator of the appropriate embryo-maternal environment during early preimplantation embryo development.

Morphological evaluation of Day 8 embryos developed during induced aluteal cycles in the mare.

A novel in vivo model utilizing serial administrations of PGF2α to induce aluteal cycles in the mare was used to evaluate the effects of progesterone-deprivation on the morphology of in vivo preimplantation embryos. We hypothesized that equine embryos produced during induced aluteal cycles (AL) would be developmentally affected, characterized by earlier embryo stage at collection, smaller embryo diameter, and lower quality grade, compared with those collected on the same day post-ovulation from control cycles during diestrus (high progesterone; > 4 ng/mL). Seven cyclic mares with a median age of 6.5 years (range 3-16) were utilized in a crossover design. Mares in estrus were artificially inseminated to a fertile stallion and randomly assigned to control or AL groups. Mares received either saline solution (control mares) or PGF2α (AL mares), twice daily on days 0, 1, and 2 and once daily on days 3 and 4. Serial blood samples were collected daily during estrus and until the day of embryo collection 8 days after ovulation. Mares were monitored until they returned to estrus, and artificially inseminated. Mares were switched to the opposite treatment group only after a successful embryo collection occurred during the previous cycle. Only cycles that produced embryos were used for analyses. No significant rise in progesterone was observed in the AL group with mean concentrations of plasma progesterone remaining <1.0 ng/mL from ovulation until embryo collection on Day 8. This is in sharp contrast to the control (luteal) cycle where a post-ovulatory rise in plasma progesterone was observed. The mean daily concentrations of plasma progesterone were significantly higher in control vs. AL group beginning at Day 3 and remained so until Day 8. The mean (±SEM) embryo diameter of AL embryos was 171 ± 5 µm compared to 756 ± 99 µm for control embryos. The majority of the Day 8 AL embryos were classified as morulas (3/9) or early blastocysts (5/9) with only 2 embryos of quality grade 1 compared to the Day 8 control embryos that were mostly expanded blastocysts (6/7) with 5 of 6 being of quality grade 1. This study shows that serial administrations of PGF2α were able to prevent significant rises in plasma progesterone, thus inducing aluteal cycles characterized by a progesterone-deprived environment for developing embryos. Embryos collected from induced aluteal cycles were adversely affected as demonstrated by a lower quality grade, smaller diameter and earlier embryo stage at collection when compared to control embryos.

Antiluteogenic effects of serial prostaglandin F2α administration in cycling mares.

A single dose of PGF2α does not consistently induce luteolysis in the equine CL until at least 5 days after ovulation, leading to the erroneous assumption that the early CL is refractory to the luteolytic effects of PGF2α. We hypothesized that serial administration of PGF2α in early diestrus would induce a return to estrus similar to mares treated with a single injection in mid-diestrus, and fertility of the induced estrus would not differ. The objectives of the study were to evaluate the effects of the 2 approaches as reflected by: (1) concentrations of plasma progesterone; (2) interovulatory and treatment-to-ovulation intervals; (3) the proportion of mares pregnant after artificial insemination. The study consisted of a balanced crossover design in which 10 reproductively normal Quarter Horse Mares were exposed to 2 treatments on 2 consecutive reproductive cycles. At detected ovulation (Day 0), mares were randomly allotted to 1 of 2 treatment groups: I, mid-diestrus treatment, administration of a single 10-mg dose of dinoprost tromethamine (PGF2α) im on Day 10; II, early diestrus treatment, administration of 10-mg PGF2α im twice daily on Days 0, 1, and 2 and once daily on Days 3 and 4. Mares in estrus and with a follicle 35 mm or greater in diameter were artificially inseminated with at least 2 billion motile sperm from a fertile stallion. Pregnancy was defined as detection of a growing embryonic vesicle on 2 consecutive examinations approximately 14 days after ovulation. Serial plasma samples were collected throughout the study period, and concentration of plasma progesterone was determined by RIA. A mixed-model ANOVA for repeated measures was used to analyze hormonal data. Interovulatory and treatment-to-ovulation intervals were compared by a paired t test and fertility by a McNemar chi-square analysis. All mares in group I underwent luteolysis after PGF2α administration denoted by mean (±SD) concentration of plasma progesterone of 0.25 ± 0.21 ng/mL detected 2 days after treatment. In group II, mean concentration of plasma progesterone remained below 1.0 ng/mL during treatment and until the onset of the next estrus. The mean interovulatory interval in group I was 18.5 ± 2.0 days compared with 13.1 ± 3.7 days in group II (P < 0.01). Treatment-to-ovulation intervals were 8.5 ± 2.0 days and 13.1 ± 3.7 days for groups I and II, respectively (P < 0.05). In both groups, 9 of 10 mares were pregnant (P = 1.0). Serial PGF2α administration beginning at ovulation consistently prevented luteal function in 10 of 10 mares in the present study without adversely affecting pregnancy rate of post-treatment cycles.