Apelin system is differentially expressed in the female reproductive organs of ewes during different reproductive stages

Introduction: The adipokine apelin seems to have a pivotal role in the control of female reproduction regulating gonadotropin release and steroidogenesis. The apelin system was also evidenced in the female reproductive tissues even if differences emerged among species. In this work, the expression of apelin and its receptor were evaluated in the ewe genital system tissues. Materials and Methods: Apelin and apelin receptor (APLNR) were investigated by RT‐PCR and immunohistochemistry in the ovary, oviduct and uterus of 10 ewes reared in a semi‐natural pasture. Tissues were collected after slaughter in July (5 ewes) and in September (5 ewes). Concentrations of plasma apelin were evaluated during the grazing period on 5 animals every 15 days. Data were examined by ANOVA followed by the Student‐Newman Keuls t test. Results: Ewes slaughtered in July were found to be in the anestrous phase while, the second group were in the luteal phase. In the ovary, the corpus luteum showed a strong positivity for APLNR while the other structures appeared negative. Apelin and APLNR were observed in the lining epithelium of oviduct and uterus and in the uterine glands. Transcripts for both molecules were evidenced in the organs examined. In the oviduct and uterus, the highest level of molecule mRNA was detected in the luteal phase of the estrous cycle, where its relative content was respectively 3 and 2‐fold higher (P < 0.05) than in the anestrous phase. Pasture dryness had no effects on the plasma apelin levels, being fairly constants during the period evaluated. Conclusion: This work described the apelin system in the ewe genital system tissues and suggests that apelin is involved in the reproduction function, being differentially expressed in the ovary, oviduct and uterus. The variations observed could be related to the reproductive apparatus cyclic activity