Localization of Inhibin [alpha]-, [beta]A- and [beta]B-Subunits and Aromatase in Ovarian Follicles with Granulosa Theca Cell Tumor (GTCT) in 6 Mares

To clarify the morphological and immunohistochemical characteristics in mares with granulosa theca cell tumor (GTCT), the localization of inhibin subunits (α, βA, βB) and aromatase in the granulosa cell layers and theca layers in the ovarian follicles were determined by immunohistochemical staining. The follicles were obtained from the ovaries of 6 mares with GTCT and 4 normal mares as controls. Immunohistochemically, inhibin α-subunit was localized in the granulosa cells of all follicles showing different sizes in all GTCT cases and βA- subunit was localized in two GTCT cases in all sized follicles. But inhibin βB- subunit and aromatase were not localized in GTCT cases. On the other hand, inhibin α-, βA-, and βB-subunits and aromatase were localized in the large and medium sized follicles, but inhibin βA- and βB-subunits and aromatase were not stained in the small sized follicles in normal cases. These findings suggest that some mares with GTCT can secrete dimeric inhibin (inhibin A), but all GTCT cases cannot secrete inhibin B. By the results of aromatase staining it is clear that testosterone is not converted into estradiol due to the lack of aromatase in the GTCT follicles.