Expression of monocyte chemoattractant protein-1 in the bovine corpus luteum around the time of natural luteolysis.

Monocyte chemoattractant protein (MCP-1) is a specific chemoattractant for monocytes/macrophages that could have a role in the influx of macrophages into the corpus luteum (CL) during structural luteolysis. In this study, reverse transcription-polymerase chain reaction and in situ hybridization were used to investigate MCP-1 mRNA expression in CL collected from 18 heifers between Days 15 and 20 of the estrous cycle. There was expression of mRNA encoding MCP-1 in luteal tissue from all cows; however, expression was greater in animals that had undergone luteolysis at the time of CL collection as compared to animals in which the CL was still functional. Similarly, in situ hybridization showed greater expression of mRNA encoding MCP-1 in CL after functional luteolysis. There was also evidence of increased MCP-1 mRNA expression in an animal with a functional CL where the systemic concentration of prostaglandin F2alpha metabolite was high at the time of tissue collection. T lymphocyte populations, identified by immunohistochemistry, had a distribution similar to that of cells expressing MCP-1 mRNA within the CL, but other cell types were also involved. These results demonstrate an increase in MCP-1 mRNA after functional luteolysis in the cow, which may be related to the influx of macrophages that occurs at this time.