Expression of Adiponectin and its Receptors in the Porcine Hypothalamus During the Oestrous Cycle

Abstract

Adiponectin is a hormonal link between obesity and reproduction, and its actions are mediated by two types of receptors: adiponectin receptor 1 (AdipoR1) and adiponectin receptor 2 (AdipoR2). This study compares the expression levels of adiponectin and adiponectin receptor mRNAs and proteins in selected areas of the porcine hypothalamus responsible for GnRH production and secretion: the mediobasal hypothalamus (MBH), pre-optic area (POA) and stalk median eminence (SME). The tissue samples were harvested on days 2-3, 10-12, 14-16 and 17-19 of the oestrous cycle. Adiponectin mRNA expression in MBH was significantly lower on days 14-16, whereas in SME, the most pronounced gene expression was found on days 2-3 of the cycle (p<0.05). Adiponectin protein in MBH was most abundant on days 17-19 and in POA on days 2-3 (p<0.05). Adiponectin protein expression in SME was at similar level throughout the most of the cycle with a statistically significant drop (p<0.05) on days 14-16. AdipoR1 gene expression in POA was potentiated on days 2-3 and 10-12 of the oestrous cycle (p<0.05). In SME, the highest AdipoR1 mRNA expression was noted on days 2-3 (p<0.05). The concentrations of the AdipoR1 protein in POA were similar throughout the luteal phase (days 2-14 of the cycle), and they decreased on days 17-19 (p<0.05). In SME, AdipoR1 protein expression peak occurred on days 2-3 (p<0.05). The expression patterns of the AdipoR2 gene in MBH, POA and SME revealed the highest mRNA levels on days 2-3 of the cycle (p<0.05). The highest content of AdipoR2 protein in MBH was reported on days 2-3 (p<0.05), while in POA on days 17-19 and in SME on days 10-12 and 14-16 (p<0.05). This study demonstrated that adiponectin and adiponectin receptor mRNAs and proteins are present in the porcine hypothalamus and that their expression levels are determined by the pig's endocrine status related to the oestrous cycle.