Expression of adiponectin receptors 1 (AdipoR1) and 2 (AdipoR2) in the porcine pituitary during the oestrous cycle

BACKGROUND Adiponectin, protein secreted mainly by white adipose tissue, is an important factor linking the regulation of metabolic homeostasis and reproductive processes. The biological activity of the hormone is mediated via two distinct receptors, termed adiponectin receptor 1(AdipoR1) and adiponectin receptor 2 (AdipoR2). The present study analyzed mRNA and protein expression of AdipoR1 and AdipoR2 in the anterior (AP) and posterior (NP) pituitary of cyclic pigs. METHODS The total of 20 animals was assigned to one of four experimental groups (n=5 per group) as follows: days 2-3 (early-luteal phase), 10-12 (mid-luteal phase), 14-16 (late-luteal phase), 17-19 (follicular phase) of the oestrous cycle. mRNA and protein expression were analyzed using real-time PCR and Western Blot methods, respectively. RESULTS The lowest AdipoR1 gene expression was detected in AP on days 10-12 relative to days 2-3 and 14-16 (p<0.05). In NP, AdipoR1 mRNA levels were elevated on days 10-12 and 14-16 (p<0.05). AdipoR2 gene expression in AP was the lowest on days 10-12, and an expression peak occurred on days 2-3 (p<0.05). In NP, the lowest (p<0.05) expression of AdipoR2 mRNA was noted on days 17-19. The AdipoR1 protein content in AP was the lowest on days 17-19 (p<0.05), while in NP the variations in protein expression levels during the oestrous cycle were negligible. AdipoR2 protein in AP was most abundant on days 10-12, and it reached the lowest level on days 2-3 and 17-19 of the cycle (p<0.05). The presence of AdipoR2 protein in NP was more pronounced on days 10-12 (p<0.05). CONCLUSIONS Our study was the first experiment to demonstrate that AdipoR1 and AdipoR2 mRNAs and proteins are present in the porcine pituitary and that adiponectin receptors expression is dependent on endocrine status of the animals.