Catechin induced modulation in the activities of thyroid hormone synthesizing enzymes leading to hypothyroidism.

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.

Effect of green tea (Camellia sinensis L.) extract on morphological and functional changes in adult male gonads of albino rats.

Green tea, prepared from the steamed and dried leaves of the shrub Camellia sinensis, is known for its antioxidant and anti-carcinogenic effects. However, its effects on male gonadal functions have not been explored adequately and the present investigation has been undertaken to evaluate the effect of green tea extract on gonads of adult male albino rats. Results of in vivo studies showed that green tea extract (GTE) at mild (1.25 g%, identical to 5 cups of tea/day), moderate (2.5 g%, identical to 10 cups of tea/day) and high (5.0 g%, identical to 20 cups of tea/day) doses, for a period of 26 days, altered morphology and histology of testis and accessory sex organs. A significant dose-dependent decrease in the sperm counts, inhibited activities of testicular delta(5)3beta-and 17beta-hydroxysteroid dehydrogenase (delta5-3beta3-HSD and 17beta3-HSD respectively) and decreased serum testosterone level were noticed. Significant increase in serum LH level was observed after moderate and high doses; serum FSH level also increased but not significantly. Histopathological examination showed inhibition of spermatogenesis evidenced by preferential loss of matured and elongated spermatids. Results of this study showed that GTE at relatively high dose may cause impairment of both the morphological and normal functional status of testis in rodents and thus its consumption at relatively high doses raises concern on male reproductive function in spite of its other beneficial effects.

Effect of different doses of un-fractionated green and black tea extracts on thyroid physiology.

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.

Goitrogenic/antithyroidal potential of green tea extract in relation to catechin in rats.

Catechins are flavonoids found in abundance in green tea, have elicited high interest due to their beneficial effects on health. Though flavonoids have been reported to have an antithyroid effect and also to be goitrogenic there have been no reports about the effect of green tea on rat thyroid. The present study was designed to examine whether high doses of green tea has any harmful effect on thyroid physiology. For this purpose green tea extract was administered orally to male albino rats for 30 days at doses of 1.25 g%, 2.5 g% and 5.0 g%, respectively. Similarly, pure catechin was administered at doses of 25, 50 and 100mg/kg body weight which is equivalent to above doses of green tea extract. Lower body weight gain associated with marked hypertrophy and/or hyperplasia of the follicles was noted in the high dose of green tea and catechin treated groups. Decreased activity of thyroid peroxidase and 5'-deiodinase I and substantially elevated thyroidal Na,K+ATPase activity have been observed. Moreover, serum T3 and T4 levels were found to reduce followed by significant elevation of serum TSH. Taken together, these results suggest that catechin present in green tea extract might behave as antithyroid agent and possibly the consumption of green tea at high dose could alter thyroid function adversely.