206 K. Sugimoto et al. In addition, the consumption of free fructose has exponen- tially increased since high-fructose corn syrups (HFCSs) began to be used as sweeteners in soft drinks and processed foods [1, 2]. In the United States of America, added sugars account for more than 30% of the calorie intake of heavy consumers of soft drinks, and it is presumed that these consumers ingest approximately 100 g/day of fructose [3]. Fructose is more lipogenic than glucose, and serum and hepatic triacylglycerol concentrations are significantly elevated after excessive consumption of sucrose or fructose [4]. The increased consumption of dietary fructose may be one of the factors that contributes to the development of obesity and the abnormalities that accompany the insulin- resistance syndrome [5–7]. Emerging evidence suggests that excessive consumption of dietary fructose is an important factor contributing to the increased prevalence of metabolic syndrome among people in the United States. In addition, the incidence of soft-drink ketosis, which is caused by frequent long-term consumption of commercial beverages containing HFCS, has increased among young obese men in Japan [8, 9]. A position state- ment issued by the American Diabetes Association dis- courages the use of fructose as a sweetener in the diet of a diabetic patient because fructose adversely affects serum lipid concentrations [10]. The adverse effects of dietary sucrose can be prevented by inhibiting the sucrase reaction in the small intestine [11]. However, sucrase inhibitors are ineffective when HFCSs are consumed as sweeteners. The evergreen tree Eucalyptus globulus is native to Australia and is widely distributed around the world. In South America and Africa, the leaves of this plant, from which tea is made, are used as a traditional remedy for diabetes. The antihyperglycemic effect of E. globulus leaf extract (ELE) has been confirmed in mice with streptozotocin-induced diabetes [12]. Furthermore, in a previous study [13], we reported that the aqueous ethanolic extract of eucalyptus leaves reduces intestinal fructose absorption and thereby inhibits the development of fatty liver, the accumulation of visceral fat, and the increase in serum triglyceride concentra- tions induced by excessive sucrose consumption, although the active ingredients of ELE have not yet been identified. To the best of our knowledge, no agents other than ELE that specifically inhibit intestinal fructose absorption have been identified thus far. In the abovementioned study, we evaluated changes in the fructose content of the portal blood by using an enzymatic method [13], which is not highly specific for fructose. Further, the effect of ELE on circulating blood has not yet been investigated. Because of these reasons, in this study, we used a highly sensitive method [14] to accurately measure the postprandial fructose concentrations in serum derived from portal and cardiac blood after the oral administration of sucrose with or without ELE in rats (Study 1). The effects of ELE on changes in the peripheral serum fructose concen- tration (SFC) were also estimated (Study 2). Materials and Methods Preparation of ELE ELE was prepared according to a previously described method [13]. The composition of ELE used in the study was as follows: total polyphenols measured as tannic acid equivalents (Folin-Ciocalteu’s method) [15], 30%; moisture (normal pressure at 105°C and 3 h), 3.0%; ash (produced by direct ashing), 5.7%; protein measured as leucine equivalents (Kjeldahl method), 1.6%; and lipid (Röse- Gottlieb method), 5.7%. Experimental animals Male Wistar rats (age, 8 weeks) were purchased from Kiwa Laboratory Animals (Wakayama, Japan). The animals were housed in cages (4–5 per cage) under standard labo- ratory conditions of a 12/12-h light-dark cycle (light phase beginning at 6.00 AM), an ambient temperature of 23°C ± 2°C, and humidity of 60% ± 10%. All animals received a standard diet (CE-2, Clea Japan Inc., Tokyo, Japan) and water ad libitum for at least 1 week prior to the study. All experimental procedures involving the laboratory animals were approved by the Animal Care and Use Committee of Osaka Prefecture University. In this study, we performed the 2 following experiments: Effect of ELE on changes in postprandial fructose concen- trations in serum samples derived from portal and cardiac blood (Study 1) Rats (body weight, 271 ± 23 g; n = 31) were starved for 16 h. Twenty-five rats were orally administered water (control group) or an ELE suspension (ELE group; 1 g/kg body weight, dissolved in 0.5 mL water). After 10 min, these rats were orally administered a sucrose solution (2 g/kg body weight, dissolved in 0.5 mL water). Under diethyl ether anaesthesia, portal and cardiac blood were sampled from the portal vein (approximately 100 μL) and the heart (>1 mL) 30 and 60 min after the sucrose ingestion. Six rats in the fasting state were operated on under diethyl ether anaesthesia, and their portal and cardiac blood were sampled. Effect of ELE on changes in postprandial fructose concen- trations in peripheral serum (Study 2) An oral sucrose-tolerance test was conducted using the same protocol as in Study 1. In brief, rats (body weight, 274 ± 21 g; n = 10) were fasted and orally administered water or the ELE suspension. After 5 min, these rats were orally administered the sucrose solution. Before the admin- istration of the test sample, and 30 and 60 min after sucrose J. Clin. Biochem. Nutr.