Estrous cycles in mares have several unique characteristics, including the presence of a long period of estrus and the absence of a typical LH surge. Like follicles of other species, equine preovulatory follicles are characterized by their ability to secrete large amounts of 17 beta-estradiol, but it is not clear which follicular cell type is responsible for estradiol synthesis in mares. To better understand the relative roles of theca interna and granulosa cells in follicular steroidogenesis, presumptive ovulatory follicles were obtained from mares during early estrus (first or second day of estrus; n = 4) and during late estrus (fourth or fifth day of estrus; n = 4). Preparations of theca interna and granulosa cells were cultured for 3 days in medium with or without equine LH, FSH, LH plus FSH, or CG (100 ng/ml) in the presence or absence of 0.5 microM testosterone, and culture media were assayed for progesterone, androstenedione, and 17 beta-estradiol. Progesterone was the predominant steroid secreted by granulosa cells in the absence of exogenous testosterone. Its accumulation was significantly higher in cultures of granulosa cells from late vs. early estrus (P less than 0.05), and all gonadotropins stimulated progesterone secretion at both stages of follicular development (P less than 0.05). In contrast, granulosa cells secreted very low amounts of androstenedione in vitro, and only very small amounts of 17 beta-estradiol were produced when cells were cultured in medium without testosterone. However, the addition of testosterone caused a 170-fold increase over control values in estradiol accumulation over 3 days of culture (P less than 0.0001), clearly indicating the presence of a very active aromatase enzyme system in equine granulosa cells. Steroid secretion by theca interna differed in several respects from secretion by granulosa cells. Theca interna from early and late estrous follicles secreted negligible amounts of progesterone in vitro, and equine gonadotropins had no effect on its secretion. Also, theca interna secreted only small amounts of estradiol in vitro, and its accumulation was not increased by the addition of exogenous testosterone. Also, in contrast to granulosa cell cultures, androstenedione was the predominant steroid secreted by theca interna from early and late estrous follicles. In conclusion, this study does not support the current model of equine follicular steroidogenesis, which holds that 17 beta-estradiol biosynthesis derives primarily from the theca interna layer.(ABSTRACT TRUNCATED AT 400 WORDS)

Here, we show for the first time that the novel inhibin/activin-betaC and -betaE subunits are expressed in normal human endometrium and the estrogen receptor positive human endometrial carcinoma cell line Ishikawa using RT-PCR and immunohistochemical detection methods. Interestingly, the Ishikawa minus cell line (lacking estrogen receptor expression) demonstrated no to minimal expression of the betaC subunit as observed with immunofluorescence and RT-PCR, suggesting a possible hormone- dependency of this subunit in human endometrial cancer cells. Moreover, because the Ishikawa cell line minus is thought to be a more malignant endometrial cell line than its estrogen receptor positive counterpart, inhibin-betaC subunit might be substantially involved in the pathogenesis and malignant transformation in human endometrium.

We demonstrated that inhibin-betaE is expressed in normal and pathological human placenta tissues. Although the precise role of this novel inhibin subunit for human placenta development is quite unclear, similarities with the well-characterized betaA- and betaB-subunits suggest an involvement in autocrine/paracrine signaling pathways, angiogenesis, decidualization and tissue remodeling under normal as well as malignant conditions. Additionally, the human chorionic carcinoma cell lines JEG and BeWo synthesize this subunit and therefore can be used as a cell culture model for further functional analysis of this subunit in human placental tissue.

(JM) S U M M A R Y Inhibins and activins are important regulators of the female reproductive system. A novel inhibin subunit, named bC, has been identified and demonstrated to be expressed in several human tissues. We demonstrate here that inhibin bC is expressed in human placenta. Expression of the inhibin bC subunit was demonstrated at the protein level by means of immunohistochemical evaluation and at the transcriptional level by an inhibin bC-specific RT-PCR analysis. Expression of inhibin bC was detected in the human chorionic carcinoma cell lines JEG and BeWo. Although the precise role of this novel inhibin subunit in human placenta development and homeostasis is unclear, analogies with other inhibin subunits and the strong expression of bC in normal human trophoblast cells and chorionic carcinoma cells suggest that bC may be involved in autocrine/paracrine signaling pathways, angiogenesis, decidualization, and tissue remodeling under normal and malignant conditions. Additionally, JEG and BeWo express bC and, therefore, can be used as a cell culture model for further functional analysis of this subunit in the human placenta. (J Histochem Cytochem 58:751-757, 2010)