Expression of oestrogen and progesterone receptors in the gilt uterus at different stages of the oestrous cycle

Ovarian steroid hormones are known to be an important modulator in the regulation of reproductive function in the female. The levels of oestrogen and progesterone have been well documented whilst interacting during the entire oestrous cycle but their specific receptors in the target cells are less understood. Therefore, a comparative study of oestrogen (ER) and progesterone receptors (PR) at certain oestrous stages should be of help in the prediction of their interaction in specific uterine compartments. Tissue samples were collected at different stages of the oestrous cycle: oestrus (n=3), early dioestrus (n=3) and late diestrus (n=3). They were fixed in 10 percent formaldehyde and embedded in paraffin. Immunohistochemistry was done, using mouse monoclonal antibodies against the oestrogen receptor (ER-6F11) and the progesterone receptor (PGR-312). In general, most of the uterine cells stained positive but with a different intensity. During oestrus, both ER and PR were obviously strong in the epithelia and the myometrium. For the glandular epithelium (GE), all GE cells stained positive for ER whereas a lower proportion of positive cells was observed for PR. During early dioestrus, it was interesting that cytoplamic staining was observed in the epithelia but not for PR staining. When comparing both receptors during early dioestrus, a stronger intensity was observed in all compartments for PR, especially in the myometrium. During late dioestrus ER and PR, expression showed no difference and every compartment of the uterus stained weaker for both receptor proteins. To summarize, the results from this study showed that both ER and PR may be regulated by the same mechanisms in some compartments and at specific stages of the oestrous cycle and that each compartment of the uterus had a different expression of ER and PR which could accord with their different roles in reproductive physiology.