In the first report (Journal of Clinical Pharmacology 2000; 40:647-654), it was shown that ingestion of 120 mg of Ginkgo biloba extract (EGb 761) daily for 3 months by normal glucose-tolerant individuals caused a significant increase in pancreatic β-cell insulin and C-peptide response, measured as the area under the curve (AUC0→120) during a 2-hour standard (75 g) oral glucose tolerance test (OGTT). This follow-up study was designed to determine the effect of the same Ginkgo biloba treatment on glucose-stimulated pancreatic β-cell function in non-insulin-dependent diabetes mellitus (NIDDM) subjects. In diet-controlled subjects (fasting plasma glucose [FPG], 117 ± 16 mg/dl; fasting plasma insulin [FPI], 29 ± 8 μU/mi; n = 6), ingestion of Ginkgo biloba produced no significant effect on the insulin AUC0→120(193 ± 53 vs. 182 ± 58 μU/ml/h, before and after ingesting Ginkgo biloba, respectively). In hyperinsulinemic NIDDM subjects taking oral hypoglycemic medications (n = 6) (FPG 143 ± 48 mg/dl; FPI 46 ± 13 μU/ml), ingestion of Ginkgo biloba caused blunted plasma insulin levels from 30 to 120 minutes during the OGTT, leading to a reduction of the insulin AUC0→120 (199 ± 33 vs. 147 ± 58 μU/ml/h, before and after Ginkgo biloba, respectively). The C-peptide levels increased, and so the AUC0→120 did not parallel the insulin AUC0→120, creating a dissimilar insulin/C-peptide ratio indicative of an enhanced hepatic extraction of insulin relative to C-peptide. Thus, in pancreatic β-cells that are already maximally stimulated, ingestion of Ginkgo biloba may cause a reduction in plasma insulin levels. Only in NIDDM subjects with pancreatic exhaustion (FPG 152 ± 46 mg/dl; FPI 16 ± 8 μU/ml;n = 8), who also took oral hypoglycemic agents, did Ginkgo biloba ingestion significantly increase pancreatic β-cell function in response to glucose loading (insulin AUC0→120 increased from 51 ± 29 to 98 ± 20 μU/ml/h, p < 0.0001), paralleled by a C-peptide AUC0→120 increase from 7.2 ± 2.8 to 13.7 ± 6.8 (p < 0.0001). Whether this increase is due to "resuscitation" of previously exhausted islets or increased activity of only the remaining functional islets is unclear. However, not even in this group did increased pancreatic β-cell activity cause a reduction of blood glucose during the OGTT. It is concluded that ingestion of Ginkgo biloba extract by an NIDDM subject may increase the hepatic metabolic clearance rate of not only insulin but also the hypoglycemic agents. The result is reduced insulin-mediated glucose metabolism and elevated blood glucose.
ASJC Scopus subject areas
- Pharmacology (medical)