Corpus Luteum Function and Its Morphological Characteristics in Cattle

Abstract

The present study was carried out to clarify the morphological and functional characteristics of the corpus luteum during the estrous cycle in cattle. The major findings are summarized as follows: 1) Morphological and endocrinological characteristics of corpora lutea corresponded to each other in the different luteal stages. During the endocrinologically active stage, the corpus luteum consists mainly of luteal tissue, in which active luteal cell types I, II and III dominate. Total progesterone concentration of the corpus luteum correlates with the appearance rate of the luteal cell type I, II and III (r=0.69, r=0.85, r=0.67, respectively). 2) A transrectal real-time B mode linear scanner was used to deterime whether the appearance of a cavity in the corpus luteum in cows causes in fertility. The mean period for return to estrus, mean serum progesterone concentration and mean pregnancy rate were not significantly different for cows that had a corpus luteum with or without a cavity. These results suggest that the cavity does not cause in fertility. 3) Specific receptors for oxytocin (OT) on intact luteal cells are demonstrated. Significant binding of OT was observed at all luteal stages. The receptors were localized on both large and small luteal cells by immunohistochemistry. OT binding was maximal at the mid-luteal stage. Furthermore, the specific binding in cultured bovine luteal cells increased dose-dependently with PGF_{2 α}. When PGF_2α synthesis in the cultured cells was inhibited by indomethacin, the specific binding of OT decreased significantly. The overall results indicate that a direct action of OT on the bovine corpus luteum is mediated by the OT receptor in a paracrine and autocrine fashion. In addition, the results suggest that PGF_2α may be one of the potent regulators for luteal OT receptors in a paracrine and/or autocrine manner.