Effect of intra-uterine infusion of prostaglandin E1 on equine serum level and intra-ovulatory interval

Abstract

Prostaglandin E2 (PGE2) has important roles in the transport of early equine embryos, pregnancy maintenance and treatment of uterotubal obstruction. There is a lack of information on PGE absorption from the uterus. We hypothesized that circulating levels of PGE metabolite (PGEM) would increase ten minutes after uterine infusion of PGE1 on day (D)10 and 12 post-ovulation and frequent treatment would affect the intra-ovulatory interval (IOI). Our objective was to compare the effect of treatment and D post-ovulation on serum PGEM. A randomized study with n=4 or 5 mares per group was performed. Mares were examined using transrectal ultrasound to detect estrus, ovulation (D0) and their IOI. A pre infusion jugular blood sample was obtained using plain vacuum tubes and the perineum was washed. Prostaglandin E1 (2 mg in dimethylsulfoxide) (DMSO) or DMSO alone was loaded into a 0.5mL sterile insemination straw and placed in an embryo transfer gun. Mares were sedated using xylazine 0.4 mg/kg IV, a vaginal speculum was introduced, and PGE1 or DMSO was infused transcervically into the uterus every 6 hours for 4 treatments on either D10 or D12. Following infusion, the uterus was briefly massaged per rectum and a post treatment blood sample was obtained 10 minutes later. There was a rest estrous cycle in between studyperiods. Serum was separated and stored at -20°C. PGEM was measured in pre and post samples using commercial enzyme-linked immunosorbent assays (ELISA) (Cayman Chemical) validated in our laboratory, according to the manufacturer's instructions. The assays had intra- and inter-assay CVs of 7.3 and 11%. Data were evaluated for normality. Statistical analyses were performed using StatPlus v8 using Kruskal-Wallis tests at P<.05 to compare the overall median Post – Pre PGEM level of the 4 time points. The median Post-Pre PGEM pmol/L(quartiles) were: D10 DMSO -10.9 (-21.5, -1.6); D10 PGE1 2920.7 (1774.5, 3990.8), DMSO D12 -13.8 (-22.8, -3.7); PGE1 D12 703.5 (677.2, 1510.5). The median IOI days (quartiles) were: D10 DMSO 25.5 (24.5, 26.5); D10 PGE1 23 (21.5, 24.3); D12 DMSO 22 (21.3, 22); D12 PGE1 22.5 (20.8, 23.2). Post – Pre median PGEM level was greater in PGE1 than DMSO treated mares on D10 (P =.021) and D12 (P =.021). On D10 16/16, and D12 12/16 infusions of PGE1 resulted in a >2fold increase in PGEM within 10 minutes. There was no effect of treatment on IOI, and no effect of D post-ovulation on PGEM. There is rapid absorption of PGE1 from the uterus, however at the dose and frequency used in this study there was no apparent effect on luteal function.