br Materials and methods br Results br Discussion In

Materials and methods
Results
Discussion In this study, we have demonstrated that the adiponectin system (genes and proteins) is present in the porcine endometrium (epithelial glandular cells, luminal epithelial Sulfamethazine and stromal cells) and myometrium (longitudinal and circular muscle layers) on days 2–3, 10–12, 14–16 and 17–19 of the cycle. It is worth noting that the highest adiponectin protein contents in the endometrium were observed on days 2–3 and 17–19 of the oestrous cycle, but adiponectin gene expression was lowest on the above days. Similarly to the endometrium, in the myometrium the highest adiponectin protein concentrations were noted on days 17–19 of the cycle, but the mRNA expression was lowest during the follicular phase. The reason for the differences in the expression patterns of adiponectin gene and protein remains unknown. The observed variations could be attributed to posttranscriptional processing of gene product and the presence of an intracellular regulatory mechanism of the gene expression. To date, the expression of adiponectin receptors (mRNA only) in the porcine endometrium was analyzed by a single study (Lord et al., 2005), but unlike in our experiment, the authors did not observe the expression of adiponectin mRNA in an adult sow. This discrepancy could be attributed to methodological differences. In our experiment, we relied on real-time PCR, which is a more sensitive and reliable method than the PCR technique used by Lord et al. (2005). The results of several studies involving different species have revealed the expression of adiponectin mRNA in human endometrial epithelial and stromal cells (Takemura et al., 2006), the expression of adiponectin protein in endometrial stromal and epithelial cells and myometrial endothelial and smooth muscle cells in rabbits, and in epithelial cells of uterine glands in mice (Schmidt et al., 2008). The expression of adiponectin gene and protein was reported in the uteri of pregnant mice (Kim et al., 2011). The expression of both isoforms of the adiponectin receptors at mRNA and protein level was observed in the human (Takemura et al., 2006), rabbit and mouse endometrium (Schmidt et al., 2008). The expression of adiponectin receptors was also detected in the mouse uterus during pregnancy (Kim et al., 2011). Our findings and the result reported in studies of other species suggest that the uterus is an important source of adiponectin and that the analyzed hormone could act as an autocrine/paracrine factor in the gland to directly modulate uterine functions. The physiological role of adiponectin in the regulation of reproductive processes is poorly understood. Adiponectin knockout mice are fertile (Kubota et al., 2002, Ma et al., 2002, Maeda et al., 2002), but transgenic female mice expressing adiponectin levels two- to three-fold higher than normal circulating levels are infertile (Combs et al., 2004), which underlines the role of adiponectin as an important factor regulating reproductive processes. AdipoR1 and AdipoR2 are highly expressed in the mid-secretory phase of the menstrual cycle (Takemura et al., 2006), which is equivalent to the implantation window in humans. Serum adiponectin levels decrease in response to selected disorders of the female reproductive system, including the polycystic ovarian syndrome (Ardawi and Rouzi, 2005), endometriosis (Takemura et al., 2005), endometrial cancer (Dal Maso et al., 2004) or preeclampsia (Ouyang et al., 2007), all of which are linked with implantation failure and pregnancy loss. The above findings suggest that the secretion of adiponectin from the endometrium may be timed to optimize both uterine receptivity and blastocyst development. Kim et al. (2011) used a mouse model of delayed and activated implantation to demonstrate higher expression of adiponectin, AdipoR1 and AdipoR2 proteins in luminal epithelial cells upon the termination of delayed implantation, which suggests a putative role of adiponectin in uterine receptivity and implantation. The fact that adiponectin suppressed the proinflammatory cytokines interleukin 6, interleukin 8 and monocyte chemotactic protein 1 in endometrial epithelial and stromal cells points to the anti-inflamatory role of adiponectin in the endometrium (Takemura et al., 2006). In this study, the expression of both adiponectin receptors increased in the mid-luteal phase, which is when maternal recognition of pregnancy occurs in the pig, suggesting that adiponectin could also affect this process. Nevertheless, further studies are needed to determine the physiological role of the hormone in the reproductive system of mammals.