Eriko Ishihara

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.

Antidiabetic effect of nitobegiku in KK-Ay diabetic mice.

In the past, nitobegiku (the herb of Tithonia diversifolia (Hemsl) A. Gray) has been used as a medicinal plant for diabetes. Antidiabetic effect of the water extract of Nitobegiku (NG) was investigated in KK-Ay-mice--one of the animal models of type 2 diabetes. NG (1,500 mg/kg body weight) reduced the blood glucose of KK-Ay mice from 509 +/- 22 mg/dl to 340 +/- 14 mg/dl (p < 0.001) and also lowered the plasma insulin (p < 0.05) 7 hours after single oral administration. No change in blood glucose of NG-treated normal mice (ddY) was seen. These results support that NG improve glucose metabolism by reducing insulin resistance. Therefore, NG may be useful for treatment of type 2 diabetes.

Effect of pregnancy on insulin metabolism in spontaneously hyperensive rats

Several lines of evidence suggest that insulin resistance and/or hyperinsulinemia may play an important role in the pathogenesis of hypertension. We studied the effect of pregnancy on insulin metabolism in spontaneously hypertensive rats (SHRs) and in Wistar-Kyoto rats (WKYs) as a control. Pregnancy markedly reduced blood pressure in both strains of rats, but insulin resistance as determined by the hyperinsulinemic glucose clamp (10 mU/kg/min) increased in SHRs and was unchanged in WKYs. The plasma insulin response to an intravenous glucose challenge in SHRs was low and did not change with pregnancy. Therefore, it is suggested that the regulation of blood pressure in these animals is linked to an unknown factor rather than to insulin resistance and hyperinsulinemia. Fetuses from SHRs had a lower body weight and plasma glucose level and higher plasma insulin and pancreatic insulin levels than those from WKYs. Thus, fetal hyperinsulinemia in the SHR may be linked to the development of hypertension in adulthood.