Apelin expression in the fallopian tubes of ewes subjected to different nutritional levels: preliminary results

Introduction: Adipokines have a decisive role as a link between the subject’s energy availability and correct reproductive activity. Apelin (APLN) causes obesity increasing body weight but also leads to infertility modifying reproductive hormones in mouse (Tekin et al. Arch Physiol Biochem 2017; 123 (1) 9-15). Expression of APLN and its receptor (APLNR) was observed in different parts of the female genital system with differences among species (Pope et al. Peptides 2012; 33 139-148). In this work, the expression and localization of APLN and APLNR was analyzed in the fallopian tubes of the sheep. Materials and Methods: A group of 15 Comisana x Appenninica adult female non-lactating sheep were fed with fresh hay from June to the pasture maximum flowering (MxF). From this period to pasture maximum dryness, the control group (Cnt) was fed with fresh hay while, the experimental group (Exp) was fed with fresh hay supplemented with 600g/day/head of barley and corn (1:1). Fallopian tubes were collected and processed to perform RT-PCR and immunohistochemistry (IHC) for APLN and APLNR. Results: RT-PCR evidenced the transcripts for APLN and APLNR in all examined samples collected from sheep in anestrous (MxF group) and sheep during the estrus cycle (Cnt and Exp groups). IHC showed a positive staining for the investigated molecules in the epithelial cells of the infundibulum and isthmus. APLN staining appeared stronger in Cnt and Exp groups respect to MxF one. Conclusion: Currently, no studies describe APLN or its receptor in the fallopian tubes of any animal species. Their identification in the sheep suggests that APLN plays a role in the salpinx activity and is involved in the reproduction. This is a preliminary report that introduces APLN investigation in the sheep female genital system however, the exact role of APLN and the influence of diet needs further elucidation.