Light and electron microscopic study of thyroid follicular cells in adult albino rats following green tea administration

ABSTRACT

Green tea [GT] is one of the most popular beverages with high daily consumption worldwide. It has a rich content of polyphenols, among which catechins predominate. Its extracts are widely used as ingredients in dietary supplements, beverages, and functional foods, which may lead to a higher consumption of GT polyphenols by the general population. Recently, a relationship between GT administration and disruption of thyroid homeostasis was suggested. The goal of the study was to clarify the impact of GT administration on the histological structure of thyroid follicular cells of adult albino rats. Thirty adult male albino rats [140-160 g] were categorized into three equal groups group I served as the control group; groups II and III received 1.25 and 5.0 g% GT extract orally at a dose of 10 ml/kg body weight, respectively, every day for 30 days. At the end of the experiment, blood samples were collected from all animals for estimation of serum triiodothyronine [T[3]], thyroxine [T[4]], and thyroid stimulating hormone. Rats were then euthanized and the thyroid glands were harvested for histological examination of thyroid follicular cells by light and transmission electron microscopy. The follicular epithelial height and colloid area of thyroid follicles were morphometrically evaluated and statistically analyzed. GT in small concentrations [in group II] did not induce any significant change in hormonal, histological, and histomorphometric assessments as compared with the control group. However, some follicular cells exhibited mildly dilated rough endoplasmic reticulum and multiple lysosomes. In contrast, GT administration in group III induced hypothyroidism as evidenced by significant reduction in serum T[3] and T[4] levels along with substantial increase in thyroid stimulating hormone level compared with controls. Histologically, many follicles displayed signs of hyperactivity as evidenced by focal hypertrophy and hyperplasia of the follicular cells along with colloid depletion. Ultrastructurally, dilated rough endoplasmic reticulum and disrupted mitochondria were encountered. Some severely degenerated follicular cells were revealed as well. Histomorphometrically, there was a significant increase in the mean follicular epithelial height, whereas the colloid area was significantly lowered as compared with the respective controls. The study clearly indicates that GT in large concentrations has the potential to disrupt thyroid follicular cell structure and function