Hiroyuki Ichiki

Antidiabetic activity of a xanthone compound, mangiferin

Mangiferin (MF) isolated from Anemarrhena asphodeloides Bunge rhizome, was tested for antidiabetic activity in KK-Ay mice, an animal model of type-2 diabetes. MF lowered the blood glucose level of KK-Ay mice 3 weeks after oral administration (p < 0.01). However, no effect on the blood glucose level in normal mice was seen, indicating that MF could be useful in treating type-2 diabetes. In addition, MF improved hyperinsulinemia and, on insulin tolerance test, reduced blood glucose levels of KK-Ay mice. From these findings, it seems likely that MF exerts its antidiabetic activity by decreasing insulin resistance.

Antitussive principles of Glycyrrhizae radix, a main component of the kampo preparations Bakumondo-to (Mai-men-dong-tang)

We attempted to elucidate the antitussive principles of Glycyrrhizae radix, a main component of Bakumondo-to (Mai-men-dong-tang). Although the 50% methanol-eluted fraction (100 mg/kg, p.o.) caused a more than 60% reduction in the number of capsaicin-induced coughs, neither the water-eluted nor 100% ethanol-eluted fractions of water extract of G. radix had antitussive effects. The water extract of G. radix contained high levels of liquiritin, liquiritin apioside, isoliquiritin, isoliquiritin apioside and glycyrrhizin. On the other hand, the 50% methanol-eluted fraction contained mainly liquiritin and liquiritin apioside, but not the other compounds. Liquiritin apioside (3-30 mg/kg, p.o.), but not liquiritin, isoliquiritin, isoliquiritin apioside or glycyrrhizin, dose-dependently inhibited the number of coughs. Methysergide, a serotonin receptor antagonist, antagonized the antitussive effect of liquiritin apioside. However, the antitussive effect of liquiritin apioside was not antagonized by naloxone. Pretreatment with glibenclamide (3 mg/kg, i.p.), an ATP-sensitive potassium channel blocker, also significantly reduced the antinociceptive effect of liquiritin apioside. These results suggest that G. radix contains a potent antitussive compound, liquilitin apioside, whose antitussive effect may depend on both peripheral and central mechanisms.

Effect of Byakko-ka-ninjin-to on the efferent activity of the autonomic nerve fibers innervating the sublingual gland of the rat

The effect of intraduodenal infusion of Byakko-ka-ninjin-to (BN) on the efferent activity of the autonomic outflow to the sublingual gland was observed in the anesthetized rat. Intraduodenal infusion of BN (50-200 mg/kg) resulted in a dose-related increase in efferent activity. The enhancement of the nerve activity following administration of 200 mg/kg BN lasted longer than three hours. It was observed that the suppressive effect on efferent activity due to i.v. administration of hypertonic saline was antagonized by intraduodenal infusion of BN. From these observations it is suggested that Byakko-ka-ninjin-to acts as a facilitatory agent on salivary secretion.