No abstract

Tea is a rich source of polyphenolic flavonoids including catechins, which are thought to contribute to the health benefits of it. Flavonoids have been reported to have antithyroid and goitrogenic effect. The purpose of this study was to evaluate whether high doses of green and black tea have a harmful effect on thyroid physiology. Un-fractionated green and black tea extracts were administered orally to male rats for 30 days at doses of 1.25 g%, 2.5 g% and 5.0 g%. The results showed that green tea extract at 2.5 g% and 5.0 g% doses and black tea extract only at 5.0 g% dose have the potential to alter the thyroid gland physiology and architecture, that is, enlargement of thyroid gland as well as hypertrophy and/or hyperplasia of the thyroid follicles and inhibition of the activity of thyroid peroxidase and 5′-deiodinase I with elevated thyroidal Na+, K+-ATPase activity along with significant decrease in serum T3 and T4, and a parallel increase in serum thyroid stimulating hormone (TSH). This study concludes that goitrogenic/antithyroidal potential of un-fractionated green tea extract is much more than black tea extract because of the differences in catechin contents in the tea extracts.

Catechins, the flavonoids found in abundance in green tea, have many beneficial health effects such as antioxidative, anticarcinogenic, anti-inflammatory, antiallergic, and hypotensive properties. However, flavonoids have antithyroid/goitrogenic effect, although less information is available about the effect of pure catechin on thyroid physiology. The present investigation has been undertaken to explore the effect of catechin administration on thyroid physiology in rat model. For the in vivo experiment catechin was injected intraperitoneally (i.p.) at doses of 10, 20 and 30 mg/kg body to male albino rats for 15 and 30 days, respectively, and thyroid activities were evaluated with respect to determination of serum levels of thyroid hormones, thyroid peroxidase, 5'-deiodinase I (5'-DI), and Na(+), K(+)-ATPase activities that are involved in the synthesis of thyroid hormone. Catechin decreased the activities of thyroid peroxidase and thyroidal 5'-deiodinase I, while Na(+), K(+)-ATPase activity significantly increased in dose-dependent manner; substantial decrease in serum T3 and T4 levels coupled with significant elevation of serum TSH were also noted. Histological examinations of the thyroid gland revealed marked hypertrophy and/or hyperplasia of the thyroid follicles with depleted colloid content. In in vitro study, short-term exposure of rat thyroid tissue to catechin at the concentrations of 0.10, 0.20, and 0.30 mg/ml leads to decrease in the activities of thyroid peroxidase and 5'-deiodinase I, while the activity of thyroidal Na(+), K(+)-ATPase remains unaltered even at high concentration of catechin treatment. The present study reinforces the concept that catechin, tea flavonoids possess potent antithyroid activity as evidenced from in vivo and in vitro studies.

Alterations in duodenal immunoglobulin (Ig-)producing cells after excessive physical stress (marathon running) were studied by immunohistochemistry in 11 well-trained male adults, both shortly after running (race time, approximately 3.00 h) and later on after a "resting period" of 8-12 weeks with normal training (7-20 h/week). The ratios of IgA-, IgM- and IgG-producing cells were similar in the two biopsy specimens and virtually identical to those in eight normal duodenal controls (medians 77.6% IgA, 18.6% IgM, and 2.5% IgG). However, in the first sample the total number of positive cells per intestinal length unit was increased in five for IgA and in seven for IgM, while it was decreased in eight for IgG compared with the second biopsy. Also, the IgA cell number tended to be slightly increased immediately after the race (median 128 cells/unit) compared with that in normal controls (median 111 cells/unit); the same tendency was found for all Ig classes considered together. This apparent change was not explained by a thickening of the mucosa. Our study showed that marathon runners seem to maintain or even enhance their intestinal IgA and IgM-production, in contrast to the IgA decrease reported for other compartments such as salivary secretions and peripheral blood. The tendency to slightly increased intestinal IgA and IgM immunocyte populations in some runners might reflect a stress-induced hormonal influence on the homing of primed B cells to the mucosa, or perhaps an immune response to elevated influx of stimulatory luminal antigens.

Polyphenolic flavonoids, specially catechins are major constituents of tea. Antithyroidal and goitrogenic effect of flavonoids have been reported however such effects of green tea on thyroid physiology has not been explored earlier. Green tea is derived from the tea leaves of Camellia sinensis and widely consumed globally. The green tea extracts(GTE) at different concentrations (1.25g% a” 5 cups of tea/ day; 2.5g% a” 10 cups of tea/ day and 5.0g% a” 20 cups of tea/ day) were orally fed to male rats for 30 days. Similarly, pure catechin was administered orally to male albino rats for 30 days at doses of 25, 50 and 100 mg/kg body weight that are equivalent to above doses of green tea extract in terms of its total catechin content and the morphological and functional changes of the thyroid have been investigated. The overall results reveal that oral administration of green tea extract at 2.5g% and 5.0g% concentrations for 30 days changed the morphology and histology resembling hypertrophy of thyroid follicles with differential colloid sizes as found in hypothyroid due to environment influences associated with significant inhibited activities of thyroid peroxidase(TPO) and 5’ monodeiodinase (5’ DI1) with elevated Na+,K+ ATPase and concomitant decrease in serum thyroxine (T4), triiodothyronine (T3) and increase in serum thyrotropin (TSH) levels developing a state of absolute biochemical hypothyroidism. All these suggest that catechin present in green tea has the antithyroidal as well as goitrogenic potential and its regular consumption at relatively high doses pose a threat to the functioning of thyroid. DOI: http://dx.doi.org/10.3329/jbsp.v9i2.22807 Bangladesh Soc Physiol. 2014, December; 9(2): 105-116