Changes in the expressions of annexin A1, annexin A5, inhibin/activin subunits, and vitamin D receptor mRNAs in pituitary glands of female rats during the estrous cycle: correlation analyses among these factors

Pituitary gonadotropin secretion is regulated by several pituitary factors as well as GnRH and ovarian hormones. To elucidate the regulatory mechanisms of pituitary gonadotropin secretions, we observed changes in the mRNA levels of pituitary factors, namely annexin A1 (Anxa1) and Anxa5, inhibin/activin subunits, follistatin (Fst), and vitamin D receptor (Vdr), in female rat pituitary glands during the estrous cycle. Additionally, levels of LHβ subunit (Lhb), FSHβ subunit (Fshb), and GnRH receptor (Gnrh-r) mRNA were examined. During proestrus, Anxa1, Anxa5, Vdr, and inhibin α-subunit (Inha) exhibited the lowest levels, while during estrus, activin βB-subunit (Actbb), Lhb, and Gnrh-r were the lowest. Moreover, Fshb exhibited the highest value during metestrus, whereas Fst did not differ significantly. Correlation analyses revealed 16 statistically significant gene combinations. In particular, four combinations, namely Anxa5 and Inha, Anxa5 and Actbb, Inha and Vdr, and Inha and Actbb, were highly significant (P<0.0001), while four combinations, Anxa1 and Anxa5, Anxa1 and Vdr, Anxa5 and Vdr, and Lhb and Gnrh-r, were moderately significant (P<0.001). The remaining eight combinations that exhibited statistical significance were Anxa1 and Inha, Anxa1 and Actbb, Vdr and Actbb, Anxa1 and Fshb, Inha and Lhb, Actbb and Fshb, Actbb and Lhb, and Fst and Fshb (P<0.05). These results highlight strong correlations among Anxa1, Anxa5, Vdr, Inha, and Actbb, thereby suggesting that an interaction among ANXA1, ANXA5, and VDR may lead to further communications with inhibin and/or activin in the pituitary gland.