Rapid Accumulation of Polymorphonuclear Neutrophils in the Corpus luteum during Prostaglandin F2α-Induced Luteolysis in the Cow

Prostaglandin F(2α) (PGF(2α)) induces luteolysis within a few days in cows, and immune cells increase in number in the regressing corpus luteum (CL), implying that luteolysis is an inflammatory-like immune response. We investigated the rapid change in polymorphonuclear neutrophil (PMN) numbers in response to PGF(2α) administration as the first cells recruited to inflammatory sites, together with mRNA of interleukin-8 (IL-8: neutrophil chemoattractant) and P-selectin (leukocyte adhesion molecule) in the bovine CL. CLs were collected by ovariectomy at various times after PGF(2α) injection. The number of PMNs was increased at 5 min after PGF(2α) administration, whereas IL-8 and P-selectin mRNA increased at 30 min and 2 h, respectively. PGF(2α) directly stimulated P-selectin protein expression at 5-30 min in luteal endothelial cells (LECs). Moreover, PGF(2α) enhanced PMN adhesion to LECs, and this enhancement by PGF(2α) was inhibited by anti-P-selectin antibody, suggesting that P-selectin expression by PGF(2α) is crucial in PMN migration. In conclusion, PGF(2α) rapidly induces the accumulation of PMNs into the bovine CL at 5 min and enhances PMN adhesion via P-selectin expression in LECs. It is suggested that luteolytic cascade by PGF(2α) may involve an acute inflammatory-like response due to rapidly infiltrated PMNs.