Estradiol- and testosterone-related changes of the thyroid gland structure in aged rats

The subject of these studies was the thyroid gland of the male aged rats (24-month-old), treated with sex steroids. Estradiol-dipropionate (EDP) in a dose of 0.5 mg/animal and testosterone-propionate (TP) in a dose of 3 mg/animal were s.c. injected to male rats every second day during 30 days. The serial sections of whole thyroid gland were used for stereological analyses and determination of the following morphometric parameters: the height and volumetric density of follicular epithelium, volumetric density of colloid and interstitium, and index of activation rate. The height of follicular epithelium, its volume density, and index of activation rate were significantly reduced in all hormone-treated animals. However, the volumetric density of colloid was significantly higher in EDP- and TP-treated animals (108% and 61%, respectively) in comparison with the corresponding controls. These morphometric parameters and cytologic features of thyroid gland of aged rats after chronic treatment with sex steroids indicate that these hormones express an inhibitory effect on thyroid follicular cells, but these changes were more prominent in animals treated with EDP than in those receiving TP.