Follicular development and atresia in the ovaries of thyroxine treated juvenile rats

Abstract

The effect of early hyperthyroidism on folliculogenesis in the ovary of juvenile rats was investigated. Hyperthyroidism was induced by injection of 150 μg DL-thyroxine (DL-T 4 ) to females every other day, from the 9 th to the 29 th day of life. Twenty four hours after the last injection treated females and corresponding intact animals were sacrificed, and the ovaries were examined using standard light microscopy and semithin sections. DL-T4 caused a significant decrease of pituitary and ovary mass, compared to intact animals. The population of healthy primary follicles was increased in the ovaries of treated rats. At the same time, the total number of atretic follicles, especially growing, was also significantly increased. Antral follicles without apoptotic changes were scarcely observed. Furthermore, granulosa cells displayed morphological changes characteristic for apoptosis: widened intercellular spaces, condensation of chromatin, cellular fragmentation and formation of atretic bodies.