The immunohistochemical presence and distribution of ghrelin, apelin and their receptors in dog ovaries

New Aspects of Corpus Luteum Regulation in Physiological and Pathological Conditions: Involvement of Adipokines and Neuropeptides

The corpus luteum is a small gland of great importance because its proper functioning determines not only the appropriate course of the estrous/menstrual cycle and embryo implantation, but also the subsequent maintenance of pregnancy. Among the well-known regulators of luteal tissue functions, increasing attention is focused on the role of neuropeptides and adipose tissue hormones—adipokines. Growing evidence points to the expression of these factors in the corpus luteum of women and different animal species, and their involvement in corpus luteum formation, endocrine function, angiogenesis, cells proliferation, apoptosis, and finally, regression. In the present review, we summarize the current knowledge about the expression and role of adipokines, such as adiponectin, leptin, apelin, vaspin, visfatin, chemerin, and neuropeptides like ghrelin, orexins, kisspeptin, and phoenixin in the physiological regulation of the corpus luteum function, as well as their potential involvement in pathologies affecting the luteal cells that disrupt the estrous cycle.

Presence and expression of apelin and apelin receptor in bitch placenta

Apelin is a potent inotropic agent causing endothelium-mediated vasodilation and is involved in vessel formation by interacting with a specific receptor. Its cardiovascular profile suggests a role in the regulation of gestational hemodynamic changes. The expression of apelin and its receptor has been reported in some portions of the reproductive tract of different mammalian species. As far as we know, there are no reports describing the expression of apelin and apelin receptor in bitch's placenta. Therefore, the aim of this study was to investigate, for the first time, the presence and distribution of apelin and apelin receptor in bitch placenta by molecular biology and immunohistochemical techniques. Sixteen adult female half-breed bitches were used. The animals were divided into two groups based on the stage of pregnancy: group 1 (mid-gestation n = 8) and group 2 (end gestation n = 8). These bitches were subjected to ovariohysterectomy (group1) or non-conservative caesarean section (group 2). The immunohistochemical technique revealed the presence of positive immune reaction for apelin and apelin receptor in all the samples examined at 30 days and at the end of pregnancy. In particular, apelin and apelin receptor staining was evident in the cytoplasms of cytotrophoblasts and in epithelial cells of the maternal portion. Even if not included into the structure of the placenta, the uterine glands also exhibited a positive immune reaction for apelin and apelin receptor. The RT-PCR analysis showed the presence of transcripts for apelin and apelin receptor in all the placenta samples examined. On the basis of our results it was also possible to hypothesize a potential role of apelin in the control of local placenta blood flow during pregnancy development in bitches.