Black tea, green tea, and tea polyphenols. Effects on trace element status in weanling rats.

Previous studies have shown that tea consumption can impair trace element metabolism, particularly iron status, and increase the risk of anemia in humans and animals. More recently, however, evidence has been accumulating to show that, in animals, consumption of green tea or its polyphenols is associated with a reduction of the incidence and severity of a variety of experimentally induced cancers. In this study we have monitored the growth, trace element status, including hematological parameters of weanling rats given either (1) water, (2) 1% black tea, (3) 1% green tea, or (4) 0.2% crude green tea extract as their sole drinking fluid while consuming diets containing either adequate or low amounts of iron. With the exception of manganese, none of the trace elements studied (iron, copper, zinc, and manganese) or the hematological indices measured were affected by the type of beverage supplied, even though the polyphenol extract was shown to chelate metals in vitro and all the animals fed the low iron diet were shown to be anemic. There appeared to be an effect of black and green teas on manganese balance in both the first and last weeks of the study. A lower level of brain manganese was associated with green tea consumption, and a higher level of this element in the kidneys of animals fed black tea. The results demonstrate that both black and green teas and a green tea polyphenol extract do not represent a risk to animals consuming the beverages as their sole fluid intake with respect to iron availability, although the interactions with manganese deserve further study.

Inhibition of rat yolk sac pinocytosis by cadmium and its reversal by zinc.

The effect of cadmium on the in vitro pinocytic rate of 10- and 11-day-old rat yolk sacs grown on rat serum in culture was studied using the synthetic substrate 125I-labeled polyvinylpyrrolidone. In medium containing concentrations of added cadmium similar to those achieved in serum by intraperitoneal dosing of rats, the rate of pinocytosis in vitro was decreased by up to 55%. When zinc was included in the medium as well, the effect of cadmium was markedly reduced, and the rate of pinocytosis was restored to about normal. The results of this in vitro study suggest that cadmium can limit and supply of nutrients to the rat embryo in a nonspecific manner, and that elevated levels of zinc can restore the ability of the yolk sac to accumulate substances from the surrounding medium. Whereas cadmium may act as a teratogen at a number of sites, the demonstrated effect of this metal on the yolk sac provides a new insight into what could be a primary mode of action of cadmium on fetal development.

Inhibition of carcinogenesis by tea: the evidence from experimental studies.

In its various forms, tea is one of the most widely consumed beverages in the world. Elucidation of the chemical components of tea has revealed that the beverage is a rich repository of antioxidants. Among these are the polyphenolics, common to green tea, but also found in black teas together with oxidized polymers that in part account, for the darkened color. Consumption of tea on a regular basis has been associated with reduced risk of several forms of cancer in human populations, with the strongest evidence linking green tea use to reduction in cancer risk in parts of Asia. To understand how tea prevents cancer, studies in animal carcinogenesis models have been done with very encouraging results. This review examines the available data from animal studies on the effects of tea in the prevention of cancer.

Teratogenic effect of extended administration of N-nitrosoethylurea and ethylurea/nitrite in rats.

N-Nitrosoethylurea (ENU) and ethylurea (EU) with sodium nitrite (NaNO2) were administered daily by mouth to Hooded Wistar rats. Doses ranged from 1-50 mg ENU/kg body weight (day-1) and from 20-70 mg EU/kg body weight day-1 and extended over days 7 to 16 inclusive of pregnancy. Severe teratogenesis occurred in animals which received from 10 mg ENU/kg day-1. Fetal death predominated at intakes above 12.5 mg ENU/kg body wt. Many organ systems were affected by ENU, but developmental anomalies of the nervous system were most common, especially anophthalmia and hydrocephalus. With EU and nitrite severe teratogenesis was noted at levels above 50 mg EU/kg body weight. Maximum teratogenic potency was obtained when nitrite was administered at approximately 50% of the level of the EU dose. Terata arising from treatment with EU/nitrite were similar to those caused by ENU. However, unlike ENU-treated animals, litters from the EU/nitrite study were either severely malformed or barely affected at all. The erratic nature of the teratogenesis following treatment with EU/nitrite was not influenced by the presence of food in the stomach at the time of dosing. For both substances administered over a 10-day period, the threshold dose needed for obvious teratogenicity was considerably less than in all previously reported single-dose studies.