Immunohistochemical detection of prolactin and prolactin receptor in canine and feline placentae

Abstract

Objectives: The aim was to determine the distribution of prolactin and its receptor in the endotheliochorial placentae of dogs and cats. Methods: Samples from different placentae from three dogs and two cats were processed by histological routine techniques. For immunohistochemistry, sections were deparaffinized and rehydrated; endogenous peroxidase was inhibited and antigen retrieval was carried out. For prolactin detection, a rabbit polyclonal anti-prolactin antibody was used (1/ 100, Abcam®, AB186522), whereas to detect prolactin receptor (PLR) a mouse monoclonal antibody was used (1/100, Abcam®, AB2772). Both antibodies were incubated overnight at 4ºC. Slides were incubated with anti-rabbit or anti-mouse EnVision™ detection system, respectively; 3,3- diaminobenzidine tetrahydrochloride was used as chromogen. Results: In dog placenta, prolactin was mainly evidenced in maternal endothelium and connective tissue (from endo, myo and perimetrium), while PLR was noticed in uterine gland epithelium (both deep and superficial), smooth myocytes (myometrium and vessels) and maternal endothelium. In cat placenta, decidual cells strongly expressed both prolactin and PLR, even those deep, small, early differentiated decidual cells. Glandular epithelium was unevenly labelled in this species. Conclusion: We conclude that in uterine glands the patterns of cellular death and proliferation occur asymmetrically; as in other species, the syncytiotrophoblast undergoes apoptosis, but it also remains proliferative in the mature placenta. On the other hand, contrary to what was reported in humans, the cytotrophoblast continues proliferating up to term. In late placentae proliferation of maternal endothelium is low, while apoptosis is evident in different cells of those blood vessels.