The Effects of Preovulatory Estradiol on the Uterine Environment and Conceptus Survival From Fertilization to Maternal Recognition of Pregnancy

Preovulatory estradiol has been reported to play a critical role in pregnancy establishment and embryonic survival, but the mechanism by which estradiol exerts its effects has not been well characterized. The objective of this thesis is to determine the effects of preovulatory estradiol on the uterine environment and conceptus survival from fertilization to maternal recognition of pregnancy. Beef cows/heifers were synchronized with the CO-Synch protocol and AIed (d 0). Cows were classified by estrus expression (estrus and no estrus), and uteri were flushed to collect d16 conceptuses nonsurgically (Rep 1; n = 29), or following slaughter (Rep 2; n = 37). Uterine luminal fluid (ULF) was analyzed for protein, glucose, and interferon tau (IFNT) concentrations. For replicate 1, total cellular RNA was extracted from blood leukocytes (d 16) to determine expression of interferon-stimulated genes (ISG): ISG-15, OAS-1, and MX2. For replicate 2, total cellular RNA was extracted from caruncular (CAR) and intercaruncular (INCAR) endometrial tissue to determine relative abundance of select glucose transporters (SLC2A1, SLC2A4, SLC2A5, and SLC5A1). There was no difference in conceptus recovery rate between estrus and no estrus cows (P = 0.20; 48% vs 29%) or between replicates (P = 0.46; 44% vs 33%). There were no differences between estrus and no estrus cows for ULF protein concentration (P = 0.36; 2222 ± 513 vs 1547 ± 525 mg/mL). There was no difference (P \u3e 0.20) in d 16 expression of ISG-15, OAS-1, or MX2 between estrus and no estrus cows, nor a difference between cows in which a conceptus was or was not recovered. In addition, there were no differences in IFNT concentrations in the ULF among estrus and no estrus cows (P = 0.42), nor a difference among cows that did and did not have a conceptus recovered from them (P = 0.71). Cows that exhibited estrus had greater glucose concentrations in ULF (P = 0.05; 51 ± 1.86 vs 45 ± 1.92 mg/dL) compared to no estrus cows, but there was no difference in protein concentration in the ULF (P = 0.36; 2222 ± 513 vs 1547 ± 525 mg/mL). Cows in which a conceptus was recovered had greater concentrations of protein in the ULF (P = 0.05; 2643 ± 585 mg/mL) compared to cows in which a conceptus was not recovered (1126 ± 463 mg/mL), glucose concentration was similar between groups (P = 0.29; 47 ± 2.12 vs 50 ± 1.70 mg/dL). For replicate 2, in both CAR and INCAR endometria, cows that exhibited estrus had greater abundance of SLC2A1 (P = 0.05) and SLC5A1 (P \u3c 0.04) mRNA. Presence of a conceptus tended to increase (P = 0.10) abundance of SLC5A1 mRNA in INCAR tissue, but had no effect (P \u3e 0.13) on abundance of SLC2A1 mRNA in either tissues or SLC5A1 mRNA in CAR tissue. In CAR tissue, cows from which a conceptus was recovered had decreased SLC2A4 mRNA abundance (P = 0.04), but there was no effect of estrus (P = 0.14) and no effect of estrus or conceptus in INCAR tissue. There was no difference in SLC2A5 mRNA abundance between estrus and no estrus cows (P \u3e 0.20), nor between conceptus and no conceptus cows (P \u3e 0.58) in CAR or INCAR tissue. In summary, conceptus recovery rates, IFNT, and protein concentration in ULF did not differ between cows that did or did not exhibit estrus, but ULF glucose content was greater in cows that exhibited estrus. There was no difference in ULF glucose concentration or IFNT between cows that did and did not have a conceptus, but ULF protein concentration was greater in cows from which a conceptus was recovered. Thus, there was no indication of increased conceptus survival to d 16 of pregnancy based on estrus expression, but ULF glucose and protein concentration changed based on estrus expression and conceptus presence