The Effect of a Long-acting GnRH Agonist (Deslorelin) on Estrogen Receptor Alpha (ERα) and Progesterone Receptor (PR) Expressions in Canine Mammary Tissue

The objective of this study was to evaluate the expression of estrogen receptor alpha (ER alpha) and progesterone receptor (PR) in normal mammary tissues of bitches before and after the bitch was implanted with the GnRH agonist, deslorelin. Fifteen mature bitches with no pathological condition of the mammary gland, and during anestrus, were selected and divided into two groups: five bitches were implanted with placebo (placebo group); and the ten bitches were implanted with 9.4 mg deslorelin (deslorelin group). Mammary tissues were collected from all bitches before implantation and at 2 and 12 weeks after implantation. The expressions of ER alpha and PR were investigated by using immunohistochemistry. The highest scores of both ER alpha and PR were found at 2 weeks after deslorelin implantation which differed significantly from those of other stages. At 12 weeks after implantation, ER alpha score decreased to the same level as before implantation while PR score tended to decrease, though not significantly differed from at 2 weeks after implantation. In placebo group, neither difference of ER alpha nor PR scores was observed at any time of the implantation. This finding indicated that deslorelin may effect the expression of ER alpha and PR in the bitch mammary tissue, in which it may stimulate the expression of ER alpha and PR at 2 weeks after deslorelin implantation. On the other hand, at 12 weeks after deslorelin implantation, ER alpha returned to the same level as before deslorelin implantation while PR decreased but not significantly different. This may indicate that ER alpha was more sensitive to deslorelin implantation than PR. In addition, the similar level of PR expression between the deslorelin and placebo group at 2 weeks after the implantion also suggests that some other factors besides deslorelin, or together with deslorelin, may have the effects on PR expression in the bitch mammary tissue.