Localization of inhibin subunits and steroidogenic enzymes in the various-sized antral follicles of the mare was examined. Antral follicles of four sizes (1, 2.5, 4.5 and 6 cm in diameter) were collected from the ovary and subjected to histological analysis. Inhibin α-subunit mRNA was localized in granulosa cells of follicles of all sizes, and inhibin βA-subunit mRNA was confined to granulosa cells of the 1-4.5-cm follicles. Inhibin α-subunit protein was found in granulosa cells of follicles of all classes, and theca cells of the 6-cm follicle. Inhibin βA-and βB-subunit proteins were found in granulosa cells of the 1-4.5-cm follicles, and theca cells of the 2.5-6-cm follicles despite the absence of inhibin/activin subunit mRNAs in theca cells. This suggests that inhibin and/or activin regulates the function of theca cells in a paracrine fashion. Aromatase protein was confined to granulosa cells of the 2.5-and 4.5-cm follicles, and to theca cells of the 4.5-cm follicle. Strong staining for aromatase protein was noted in the 4.5-cm follicle as compared to the 2.5-cm follicle. Positive immunostaing for 3β-hydroxysteroid dehydrogenase was observed in granulosa cells of the 2.5-6-cm follicles, and in theca cells of the 4.5-and 6-cm follicles. These data suggest that inhibin is predominantly secreted from 1-4.5-cm antral follicles and estradiol is predominantly secreted from antral follicles of about 4.5-cm in diameter. Further, it is suggested that progesterone is the predominant hormone secreted form the preovulatory follicle in the mare.
Flexor tendonitis in racehorses which is caused by racing or training diminishes their running ability. In the present study, the involvement of hyperthermia in the development of flexor tendonitis is investigated. When fibroblasts isolated from the superficial digital flexor tendon of a horse are cultured, their survival rate decreases after 1 hour of exposure to a temperature of 43°C. When a racehorse runs on a dirt track, the center of the tendon runs a fever of 43°C or more. This finding suggests that the fever occurring during running can be a cause of flexor tendonitis. The study also indicates that cooling the distal ends of the fores after racing is effective in preventing flexor tendonitis.