204 T. Matsuo and K. Izumori Table 2. Effects of D-psicose on plasma glucose concentrations (mg/dL) after oral carbohydrate loading in rats Time after administration (min) Test carbohydrates Glucose Glucose+Fructose Glucose+Psicose Sucrose Sucrose + Fructose Sucrose + Psicose Maltose Maltose + Fructose Maltose + Psicose Starch Starch + Fructose Starch + Psicose 0 99 ± 7 92 ± 8 92 ± 10 102 ± 8 102 ± 12 95 ± 9 94 ± 9 88 ± 12 87 ± 9 98 ± 10 93 ± 4 92 ± 9 30 148 ± 14 139 ± 12 140 ± 14 135 ± 13 134 ± 13 129 ± 11 146 ± 12a 140 ± 12ab 133 ± 18b 131 ± 10 128 ± 14 124 ± 11 60 157 ± 15 154 ± 17 154 ± 10 151 ± 27a 142 ± 11ab 138 ± 12b 157 ± 19 155 ± 15 149 ± 13 133 ± 18 134 ± 16 125 ± 15 90 159 ± 7 156 ± 18 154 ± 16 148 ± 14 146 ± 10 146 ± 16 163 ± 17a 152 ± 9ab 147 ± 12b 130 ± 17 127 ± 12 121 ± 12 120 168 ± 18 159 ± 18 155 ± 13 146 ± 17 144 ± 9 142 ± 17 159 ± 12a 147 ± 12ab 141 ± 16b 125 ± 19 126 ± 11 120 ± 12 ΔAUC (h·mg/dL) 6087 ± 1160 6530 ± 1194 5866 ± 1434 5235 ± 1692 4109 ± 1106 4433 ± 1654 6855 ± 1383 6386 ± 1430 5895 ± 1061 4035 ± 1233 3836 ± 1330 3098 ± 1138 Values are the means ± SD for 12 rats. Fructose and psicose (0.2 g/kg body weight) were administered with glucose, sucrose, maltose or starch (2 g/kg body weight). Means with different superscripts within a column are significantly different (p<0.05, one-way ANOVA and Fisher’s PLSD tests). randomly divided into the 12 groups shown in Table 1. Twelve rats were fasted overnight for 12 h before the experi- ments. D-Psicose, or D-fructose (0.2 g/kg) was orally admin- istered via gavage with 2 g/kg glucose, sucrose, maltose, or soluble starch. At 0, 30, 60, 90, and 120 min after loading, blood was collected from the tail vein to obtain the plasma. The plasma glucose concentration was determined by the kits (Glucose CII-Test, Wako Pure Chemical Industries). Statistical analysis All values are expressed as the mean ± SD. The data was assessed by one-way ANOVA and Fisher’s PLSD tests. All analyses were performed with a commercially available statistical package (StatView J-5.0, SAS Institute Inc., Cary, NC). Results Inhibitory effect of D-psicose on activities of α-amylases and α-glucosidases in vitro Relative enzyme activities shown in Table 1 are 100% without inhibitors (D-fructose, D-psicose, or D-allose). D- Fructose (0.4–4.0 mg/ml) showed no inhibition of each enzyme activity (Table 1). D-Psicose and D-allose (4.0 mg/ ml) significantly inhibited intestinal α-amylase, sucrase, maltase, and α-amylase from aspergillus oryzae (Table 1) except for in the maltase inhibition induced by D-allose. The inhibitory effect of D-psicose was greater than that of D-allose (Table 1). Neither D-psicose nor D-allose inhibited the pancreatic α-amylase, and α-amylase from bacillus subtilis activities (Table 1). D-Psicose (4.0 mg/ml) slightly inhibited the salivary α-amylase activity, but D-allose did not suppress this enzyme (Table 1). Effect of D-psicose on plasma glucose concentrations after carbohydrate loading in rats D-Psicose significantly suppressed the increase of plasma glucose levels after sucrose and maltose loading in fasted rats, however, no suppression was found after glucose loading (Table 2). After 60 min after ingestion, the plasma glucose concentration was significantly lower in the Sucrose + Psicose group than in the Sucrose group, the suppression lasted from 30 to 90 min in the Sucrose + Psicose group (Table 2). At 30, 90 and 120 min after inges- tion, the plasma glucose concentration was significantly lower in the Maltose + Psicose group than in the Maltose group, and the suppression lasted from 30 to 120 min in the Maltose + Psicose group (Table 2). The plasma glucose level was also suppressed by D-psicose after starch loading in fasted rats, however, the suppression was not significant. D-Fructose did not suppress the increase of plasma glucose levels after either carbohydrate loading (Table 2). Discussion We demonstrated in this study that D-psicose selectively inhibited the intestinal α-amylase, sucrase, and maltase activities. We also showed that D-psicose suppressed the increase of plasma glucose after ingestion of sucrose, maltose, and starch in rats, but the plasma glucose suppres- sion was not significant after starch ingestion. Semenza and Balthazar [23] and Seri et al. [14] reported a similar inhibi- J. Clin. Biochem. Nutr.