Antihyperglycemic and blood pressure-reducing effects of stevioside in the diabetic Goto-Kakizaki rat

Abstract

Stevioside, a glycoside present in the leaves of the plant, Stevia rebaudiana Bertoni (SrB), has acute insulinotropic effects in vitro. Its potential antihyperglycemic and blood pressure–lowering effects were examined in a long-term study in the type 2 diabetic Goto-Kakizaki (GK) rat. Rats were fed 0.025 g · kg−1 · d−1 of stevioside (purity > 99.6%) for 6 weeks. An intra-arterial catheter was inserted into the rats after 5 weeks, and conscious rats were subjected to arterial glucose tolerance test (2.0 g · kg−1) during week 6. Stevioside had an antihyperglycemic effect (incremental area under the glucose response curve [IAUC]): 985 ± 20 (stevioside) versus 1,575 ± 21 (control) mmol/L × 180 minutes, (P <.05), it enhanced the first-phase insulin response (IAUC: 343 ± 33 [stevioside] v 136 ± 24 [control] μU/mL insulin × 30 minutes, P <.05) and concomitantly suppressed the glucagon levels (total AUC: 2,026 ± 234 [stevioside] v 3,535 ± 282 [control] pg/mL × 180 minutes, P <.05). In addition, stevioside caused a pronounced suppression of both the systolic (135 ± 2 v 153 ± 5 mm Hg; P <.001) and the diastolic blood pressure (74 ± 1 v 83 ± 1 mm Hg; P <.001). Bolus injections of stevioside (0.025 g · kg−1) did not induce hypoglycemia. Stevioside augmented the insulin content in the β-cell line, INS-1. Stevioside may increase the insulin secretion, in part, by induction of genes involved in glycolysis. It may also improve the nutrient-sensing mechanisms, increase cytosolic long-chain fatty acyl-coenzyme A (CoA), and downregulate phosphodiesterase 1 (PDE1) estimated by the microarray gene chip technology. In conclusion, stevioside enjoys a dual positive effect by acting as an antihyperglycemic and a blood pressure–lowering substance; effects that may have therapeutic potential in the treatment of type 2 diabetes and the metabolic syndrome. Copyright 2003, Elsevier Science (USA). All rights reserved.