EXPRESSION OF MONOCYTE CHEMOATTRACTANT PROTEIN-1 IN THE CORPUS-LUTEUMOF THE RAT

The known accumulation of macrophages in corpora lutea (CL) at the tim e of luteal regression prompted us to investigate whether the chemoatt ractant protein monocyte chemoattractant protein-1 (MCP-1) is expresse d in the rat CL. On the day of confirmed mating (Day 0 of pregnancy), regressing CL from the previous (nonfertile) estrous cycle contained i mmunodetectable MCP-1 and numerous monocytes/macrophages, whereas the newly formed CL of pregnancy, within the same ovary, contained little MCP-1 and few monocytes/macrophages. MCP-1 diminished in the regressin g CL on Days 3 and 9 of pregnancy, although numerous monocytes/macroph ages remained. The CL of pregnancy on Days 3 and 9 of pregnancy contai ned minimal MCP-1 and relatively few monocytes/macrophages. By Days 17 and 21 of pregnancy, however, prior to parturition and prior to an ac cumulation of monocytes/macrophages, expression of MCP-1 increased in the CL of pregnancy. Northern blots revealed a resurgence of luteal MC P-1 mRNA on Day 21 of pregnancy: 3805 +/- 1077 on Day 21 vs. 1059 +/- 177 on Day 9 (p < 0.05; expressed as densitometric units relative to b eta-actin). In conclusion, the expression of MCP-1 in the rat CL in as sociation with, or preceding, the appearance of monocytes/macrophages at the time of luteal regression is consistent with the known role of MCP-1 as a potent chemoattractant for monocytes/macrophages. This sugg ests that MCP-1 might have a prominent role in the immunological proce ss of luteal regression.