Intramammary lipopolysaccharide infusion alters gene expression but does not induce lysis of the bovine corpus luteum

Abstract

Data from various studies indicate that the ovarian function in dairy cows can be compromised during intramammary infections. Therefore, in this study, we investigated if an experimentally induced mastitis has an effect on corpus luteum (CL) function in 14 lactating cows. On d 9 of the estrous cycle (d 1=ovulation), cows received a single dose of 200 μg of Escherichia coli lipopolysaccharide (LPS; dissolved in 10 mL of NaCL; n=8) or 10 mL of saline (control; n=6) into one quarter of the mammary gland. Measurements included plasma cortisol, haptoglobin, and progesterone (P4) concentrations, as well as luteal size (LTA) and relative luteal blood flow (rLBF). Sampling was performed on d 1, 4, and 8. On d 9, the main examination day, sampling was performed immediately before (0 h), every 1h (or at 3-h intervals for LTA and rLBF) until 9 h, as well as 12 and 24 h after treatment. Thereafter, measurements were taken on d 12, 15, 18, and then every 2 d until ovulation. Luteal tissue was collected for biopsy 24 h before and 6 h after treatment. Quantitative real-time PCR was applied to assess mRNA expression of steroidogenic factors (STAR, HSD3B), caspase 3, toll-like receptors (TLR2, -4), tumor necrosis factor α (TNFA), and prostaglandin-related factors (PGES, PGFS, PTGFR). Intramammary LPS infusion caused considerable inflammatory responses in the treated udder quarters. No decrease in plasma P4 concentrations was noted after LPS-challenge, and P4 levels did not differ between LPS-treated and control cows. Furthermore, LTA and rLBF values were not decreased after LPS challenge compared with the values obtained immediately before treatment. However, LPS infusion increased plasma levels of cortisol and haptoglobin compared with the control group. In the CL, mRNA abundance of TLR2 and TNFA was increased in cows after LPS-challenge (but not in control cows), whereas TLR4, steroidogenic, and prostaglandin-related factors remained similar to the mRNA abundance before treatment. In conclusion, intramammary LPS challenge induces systemic inflammatory reactions which alter the luteal mRNA abundance of TLR2 and TNFA but does not induce lysis of the CL.