Effects of repeated treatments with an extract ofGinkgo biloba (EGb 761) and bilobalide on liver and muscle glycogen contents in the non-insulin-dependent diabetic rat

Abstract

The effects of repeated (15-day) oral treatments with an extract of Ginkgo biloba (EGb 761; 50 mg/kg/day) or with its terpenoid constituent, bilobalide (2 mg/kg/day), were assessed in normal rats and in rats that had been previously injected with streptozotocin (50 mg/kg, i.p. in saline solution), a dose which provided a model of non-insulin-dependent diabetes mellitus (NIDDM). In this model of diabetes, blood glucose is significantly increased while the circulating insulin level remains unchanged. Glucose penetrates cells because of decreased glycogen turnover, a metabolic abnormality that can be revealed by using an oral glucose tolerance test (OGTT). In control rats, hyperglycemia was accompanied by increased glycogen synthesis, as evidenced by increased concentrations of this storage substance in liver and skeletal muscle. Repeated treatment with EGb 761 or bilobalide increased the glycogen contents of both liver and muscle. This effect of bilobalide was additive to that of hyperglycemia in muscle. In diabetic rats, hyperglycemia did not modify glycogen synthesis, indicating impaired glucose utilization. Repeated treatment with EGb 761 or bilobalide partially prevented this impairment and led to increased in glycogen content in both liver and muscle under control conditions an during OGTT with 2 g/kg glucose. The moleculasr mechanism underlying these actions of EGb 761 could be related to an antioxidant effect (i.e., suppression of free radical formation) or to free radical-scavenging, since EGb 761 is known to have such effects and since free radicals have been implicated in the cytotoxic activity of streptozatocin. However, the increase in glucose uptake induced by bilobalide may have been related to increased glycogen synthesis. Drug Dev. Res. 40:68–74, 1997. © 1997 Wiley-Liss, Inc.