The cellular localization of inhibin α, βA and βB subunits in cyclic ovaries of the guinea pig was investigated. The immunoreactivity of inhibin α, βA and βB subunits was localized to the granulosa cells of some large healthy follicles in each ovary throughout the estrous cycle. The number of follicles that stained was in accordance with the number of offspring typical in guinea pigs. Inhibin βB was also localized to the granulosa cells of small antral follicles on Day 4. There were two kinds of staining patterns for inhibin α, βA and βB subunits on Day 12: strongly stained follicles identical to those observed on Days 8 and 16, and weakly stained follicles that showed atresia in hematoxylin and eosin (HE) stained sections. Two types of ovarian cysts were found throughout the estrous cycle in this experiment: serous cysts and follicular cysts. The incidence of serous cysts and follicular cysts were 64% and 24% of animals, respectively. There was no positive reaction for inhibin α, βA and βB subunits in the corpora lutea, other follicles or any kind of ovarian cyst during the estrous cycle. These results comfirm that only dominant follicles stain positively for inhibin α and βA subunits and are in agreement with the phenomenon that the follicular development of guinea pigs shows two waves of growth. This study is also the first to describe the ovarian cysts during the estrous cycle in guinea pigs systematically.
