We observed larger numbers of both ED1- and ED2-positive cells per high-power field when regressing corpora lutea of all ages were addressed (experiment 1) than in corpora lutea entering regression on estrus (experiment 2). In addition, significant numbers of these immune cells were already present on proestrus when all regressing corpora lutea were used for analysis (experiment 1). This suggests that the infiltration of immune cells that occurs between proestrus and estrus is not transient and that it may continue as corpora lutea continue to regress, leading to larger numbers of monocytes/macrophages and resident, differentiated macrophages per high-power field in older corpora lutea. buy flovent inhaler
We do observe increases in ED2-positive cells in corpora lutea entering regression on estrus, as compared to proestrus. It is possible that the time required for recruited macrophages to express the ED2 antigen is decreased in cycling rats as compared to hypophysectomized rats due to differences in the steroid milieu. The hypophysectomized rat, which lacks pituitary trophic hormones, has a low level of production of estradiol and of glucocorticoids. In addition, the absence of prolactin results in the conversion of progesterone to the inactive metabolite 20a-dihydropro-gesterone by the corpora lutea. Thus the differential production of adrenal and ovarian steroids in the cycling rat as compared to the hypophysectomized rat may affect the differentiation of macrophages, at least some lineages of which express receptors for estrogens, androgens, and glucocorticoids.