The Role of Leukotriene B₄ in Cow Metritis

Metritis is a common postpartum disease in dairy cows. As a mast cell (MC) mediator, leukotriene B₄ (LTB₄) is the strongest phagocyte chemokine. It is important in inflammation for the recruitment of immune cells to resist infection. This study investigated the effect of LTB₄ in metritis.

Twenty Holstein cows 3 to 6 years old and at 6 to 10 days postpartum were selected, ten of which with postpartum metritis were the experimental group, and the other ten of which as healthy cows were the control group. The levels of LTB₄, substance P (SP) and vasoactive intestinal peptide (VIP) were measured by ELISA, the expression of LTB₄ receptor 2 (BLT2), matrix metalloproteinase (MMP)-2 and MMP-9 mRNA was measured by qPCR, and collagens I and IV were detected by immunohistochemical staining.

Concentrations of SP and LTB₄ were significantly higher, but those of VIP were significantly lower in the experimental group than those in the control group. The expression of BLT2, MMP-2 and MMP-9 mRNA was significantly higher in the experimental group than that in the control group. The expression of collagen Ⅰ and collagen Ⅳ was significantly lower in the experimental group than that in the control group.

In metritis, SP promotes the activation of MC and the synthesis and release of LTB₄. Leukotriene B₄ chemotactic immune cells promote the high expression of collagenase, which accelerated the hydrolysis of collagen, while the inhibitory effect of VIP on MC was weakened. This may further aggravate the damage to uterine tissue.