Adiponectin is an adipose-secreted hormone that regulates energy homeostasis and is also involved in the control of the reproductive system. The goal of the present study was to investigate changes in adiponectin gene and protein expression in porcine ovarian structures during the oestrous cycle and to examine the effects of in vitro administration of adiponectin on basal and gonadotrophin- and/or insulin-induced secretion of ovarian steroid hormones. Both gene and protein expression of adiponectin were enhanced during the luteal phase of the cycle. Adiponectin affected basal secretion of progesterone by luteal cells, oestradiol by granulosa cells, and testosterone by theca interna cells. The gonadotrophin/insulin-induced release of progesterone from granulosa and theca interna cells and the release of oestradiol and androstenedione from theca cells was also modified by adiponectin. In conclusion, the presence of adiponectin mRNA and protein in the porcine ovary coupled with our previous results indicating adiponectin receptors expression suggest that adiponectin may locally affect ovarian functions. The changes in adiponectin expression throughout the oestrous cycle seem to be dependent on the hormonal status of pigs related to the stage of the oestrous cycle. The effect of adiponectin on ovarian steroidogenesis suggests that this adipokine influences reproductive functions in pigs.

Adiponectin administration affected GnRH-and/or insulin-induced LH and FSH output in a manner dependent on the phase of the estrous cycle. In this study we indicated for the first time adiponectin expression in the porcine AP and NP that was dependent on the phase of the estrous cycle. In vitro studies indicated that adiponectin may affect gonadotropin secretion. The above suggests that the studied adipokine may influence female reproductive functions via its effect on LH and FSH secretion by gonadotrophs, but the cellular mechanism of its action remains unknown. luteinizing hormone; follicle-stimulating hormone

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BackgroundAdiponectin, 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.MethodsThe 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.ResultsThe 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).ConclusionsOur 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.

The aim of this study was to compare the expression levels of adiponectin receptor 1 and adiponectin receptor 2 mRNAs and proteins in porcine ovaries during four stages (days 2 to 3, 10 to 12, 14 to 16, 17 to 19) of the oestrous cycle and to measure adiponectin plasma concentrations during the same phases of the cycle. Higher mRNA expression of adiponectin receptor 1 was detected in porcine granulosa cells than in corpora lutea and theca cells (P < 0.01). In contrast, higher gene expression of adiponectin receptor 2 occurred in newly developed and mature corpora lutea (P < 0.01). The adiponectin receptor 1 protein content was the highest in corpora lutea isolated on days 2 to 3 of the cycle and was the lowest in theca interna cells (P < 0.01). The profile of adiponectin receptor 2 protein was similar to that of adiponectin receptor 1. Adiponectin plasma concentrations were significantly higher throughout the luteal phase than in the follicular phase (P < 0.01). In conclusion, the presence of adiponectin receptor 1 and adiponectin receptor 2 mRNAs and proteins in the porcine ovary suggests that adiponectin may directly affect ovarian functions through its own specific receptors. The expression of both receptors and adiponectin plasma concentration were dependent on hormonal status related to the stage of the cycle. Key words: Adiponectin receptors, adiponectin, pig, ovary, oestrous cycleAdiponectin is an adipose-secreted 244-amino-acid protein with 30 kDa molecular weight, which circulates in the blood in the form of a trimer (low molecular weight, LMW), a hexamer (middle molecular weight, MMW) or a multimer (high molecular weight, HMW) (Maeda et al., 1996). Adiponectin exerts its effect by binding to two distinct but structurally related 7-transmembrane receptors, adiponectin receptor 1 (AdipoR1) and adiponectin receptor 2 (AdipoR2).