There must also be a signal that causes increased expression of mRNA encoding MCP-1 within luteal tissue. The expression of mRNA encoding MCP-1 was significantly increased in CL from animals after functional luteo-lysis and also from one animal prior to the completion of functional luteolysis (progesterone > 1 ng/ml, cow 959, Table 1). The potentially significant finding in this individual cow was the high systemic concentration of PGFM in plasma at the time of CL collection. MCP-1 mRNA expression as demonstrated by RT-PCR and in situ hybridization was higher in this animal compared to the other pre-luteolytic cows. This suggests that PGF2a released during luteolysis may be involved in activating the expression of mRNA encoding MCP-1 in the CL. Future studies will address this hypothesis. Other factors are also likely to be involved in increased expression of MCP-1 mRNA. For example, increased amounts of tumor necrosis factor a have been measured in the bovine CL after functional luteolysis. proventil inhaler
As discussed previously, MCP-1 expression may be enhanced by this cytokine as well as other cytokines that have not been investigated in detail within the bovine CL. Declining progesterone concentrations during luteolysis may also be the stimulus for enhanced MCP-1 mRNA expression in the cow, as has been suggested in the rat. However, this appears less likely when the single cow discussed above is considered (cow 959, Table 1). The increase in MCP-1 expression occurred while progesterone concentrations were still high. It is not clear from the results of the present study whether MCP-1 is also produced by luteal cells themselves. Hos-ang et al. described expression of MCP-1 by luteal cells from the pig, but this study used dispersed luteal tissue that would contain large numbers of endothelial cells and fibroblasts that could themselves act as the source of MCP-1. In conclusion, the results of this study provide further evidence supporting a role for MCP-1 in the attraction of monocytes/macrophages into luteal tissue after functional luteolysis. Further studies are required to determine the factors involved in regulating MCP-1 expression and to establish the cell types involved.