The study was designed to determine the distribution of oestrogen receptors (OR) and progesterone receptors (PR) in specific endometrial cell populations during the oestrous cycle. Uterine biopsy samples and blood were obtained from five clinically healthy cows at Days 1 (initiation of behavioural oestrus), 8, 15 and 19 of the oestrous cycle. All animals conceived after biopsy regimen. Immunoperoxidase staining techniques at light microscopic level were used to localise OR and PR. Specific positive staining reactions for both receptors were always limited to cell nuclei. Immunoreactivity was scored semiquantitatively. In the surface epithelium, OR were detectable throughout the oestrous cycle and exhibited a significant increase from Days 8 to 15. In stromal cells and glandular epithelial cells, however, staining intensities for OR were strong at behavioural oestrus (Day 1). Significantly lower immunoreactivities were recorded at cycle Day 15. At oestrus, and to a lesser extent at Day 8, a significant gradient in oestrogen receptor content was evident, showing increasing immunoreactivity with the depth of the endometrial tissue. In surface epithelial cells, significantly more progesterone receptor immunoreactivity was evident at Day 8 as compared with Days 1, 15 and 19. In glandular epithelia, only some PR stained at oestrus, many of them occurred at Day 8 and very few could occasionally be seen at Days 15 and 19. In stromal cells, PR exhibited a somewhat different quantitative staining pattern, i.e. many occurred at Days 1, 8 and 19. A significant decrease in immunoreactivity was observed between Days 8 and 15. While occasionally recorded smooth muscle cells of the myometrium could exhibit even strong immunoreactivities for both receptors, such cells of the tunica media of blood vessels were almost devoid of OR and PR. Caruncular tissue districts, in a few cases included in biopsy specimens, did not differ substantially from intercaruncular endometrium in OR and PR contents. Endothelial cells, granulocytes and lymphocytes always were devoid of specific nuclear staining. In the present study, OR and PR contents of the bovine endometrium exhibit cell type and location specific reaction patterns during the oestrous cycle. This suggests that different cell types ab within this target organ can respond in a different manner to identical hormonal stimuli.
