The results of this study clearly indicate that regressive changes in the corpus luteum, including changes in MCP-1 and inflammatory cells, are initiated during the time period between proestrus morning (6 h prior to the proestrous prolactin surge) and estrus (16-24 h after the proestrous prolactin surge). These regressive changes are similar to those observed following treatment of hypophysectomized rats with exogenous prolactin; this is consistent with the idea that the proestrous prolactin surge might be the stimulus for inflammatory/immune events occurring in the corpora lutea during the estrous cycle. buy ventolin inhalers
The recruitment of inflammatory/immune cells into the corpus luteum at the time of luteal regression has been observed in a number of species; however, the underlying stimuli and mechanisms for this recruitment remain largely unknown. The chemokine, MCP-1, may have a prominent role. MCP-1 is expressed in the corpora lutea of several species. It has multiple roles as a che-moattractant for monocytes, and as a factor that induces the production of reactive oxygen intermediates and lysosomal enzymes by monocytes. The presence of MCP-1 staining at higher intensity and altered distribution within the corpora lutea on estrus compared to proestrus suggests that the presence of monocytes/macrophages in the corpus luteum at regression is not incidental and is associated with changes in expression of MCP-1. We have previously reported a similar association in regressing corpora lutea at the end of pregnancy, in regressing corpora lutea the day after mating, and in corpora lutea regressing due to the acute actions of prolactin injected in hypophysectomized rats.