Rapid Accumulation of Polymorphonuclear Neutrophils in the Corpus luteum during Prostaglandin F _2α-Induced Luteolysis in the Cow

Abstract

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.