Effects of chronic estradiol treatment on the thyroid gland structure and function of ovariectomized rats

ABSTRACT

Estrogen therapy is widely used nowadays in women to treat many postmenopausal symptoms but it may have some undesirable effects due to multiple organs affection. The aim of this study was to determine the effects of chronic estradiol treatment oh the structure and function of the thyroid gland in ovarictomized rats as a model simulating menopause. Thirty adult female albino rats divided into three groups were used in this study, the first group was sham-operated, while the second and third groups were ovariectomized. The first and second groups were injected with olive oil while the third group was injected with estradiol diproprionate daily for three months, after that hormonal assay for T3, T4, TSH and histological specimens of the thyroid were taken and examined by light and electron microscopy. Serum levels of T3 and T4 were significantly decreased in ovariectomized animals and increased with estradiol treatment, while TSH increased in ovariectomized animals and decreased with estradiol. Histological and morphometric study in ovariectomized group revealed marked accumulation of colloid in follicular lumens with decreased epithelial height in addition to increased connective tissue amount while with estradiol treatment the follicles were smaller with small amount of colloid with increased epithelial height in addition to decreased connective tissue content. Ultrastructural study supported these results in addition to the presence of large amount of intracytoplasmic colloid vesicles after estradiol treatment. Decreased amount of estrogen may lead to thyroid hypofunction while estradiol treatment may lead to hyperactivity so it should be used very cautiously in the treatment of postmenopausal symptoms to avoid its undesirable stimulatory effect on the thyroid