Effects of seed saponins of Thea sinensis L. (Ryokucha saponin) on alcohol absorption and metabolism.

We evaluated the effects of the seed saponins of Thea sinensis L. on alcohol absorption and metabolism in rats and mice. An ethanolic extract from the seeds of T. sinensis was orally administered to the rats 1 hr before or 0.5 hr after administration of ethanol (2 g/kg), and the blood ethanol assayed 0.5, 1, 2, 3, and 4 hr after ethanol administration. The ethanol level decreased after both pre- and post-administration of the extract. The extract was further purified to obtain a saponin fraction which was orally administered to mice 1 hr before ethanol administration. Blood, liver, and stomach were obtained 0, 1, 3, and 6 hr after ethanol administration, and the ethanol, acetaldehyde, acetate, and acetone concentrations in each specimen were measured by head space gas chromatography. The saponin fraction decreased the ethanol levels in the blood and liver but increased that in the stomach five-fold over the control level, suggesting inhibition of alcohol absorption. The ethanol disappearance time from the blood was shortened, suggesting the promotion of alcohol disappearance. The acetate and acetone levels were unaffected. However, the acetaldehyde level decreased in the blood, liver, and stomach. The decreases in the ethanol and acetaldehyde levels in the liver suggested the protective effects of the seed saponins on the liver. The saponins did not directly inhibit hepatic alcohol dehydrogenase activity. The seed saponins of T. sinensis seem to suppress alcohol absorption by slowing gastric emptying and by inhibiting absorption across the cell membranes of the digestive tract.