The expression of the aryl hydrocarbon receptor in reproductive and neuroendocrine tissues during the estrous cycle in the pig.

The aryl hydrocarbon receptor (AhR) has been recognized as a mediator of xenobiotic-induced toxicity. In addition, it was demonstrated that the AhR is able to influence the regulation of reproductive processes in females. The aim of this study was to examine AhR mRNA (real-time PCR) and protein (Western-blot) expression in ovarian follicles and stroma, corpora lutea (CL), oviducts, endometrium, myometrium as well as in medial basal hypothalami (MBH), and anterior (AP) and posterior (PP) pituitaries harvested during the follicular (days 17-19) and luteal (days 8-10) phase of the porcine estrous cycle. The AhR transcript and protein were found in all structures collected during both phases. AhR mRNA expression tended (p=0.06) to be higher in the CL than in follicles. The AhR protein expression in ovarian stroma was higher (p≤0.01) during the follicular than in the luteal phase. Endometrial expression of AhR mRNA was higher (p≤0.01), while AhR protein was lower (p≤0.01) during the follicular phase in comparison to the luteal phase. Within neuroendocrine tissues, AhR mRNA and protein content in hypothalamus were relatively low and did not differ (p>0.05) between phases. In contrast, higher AhR mRNA expression in AP (p≤0.001) and protein expression in PP (p≤0.01) were found during the luteal phase compared to the follicular phase. Differences in AhR expression observed in reproductive and neuroendocrine tissues during the follicular and luteal phase of the estrous cycle indicate the involvement of AhR in the regulation of reproductive function in pigs.