Sedative and antispasmodic effects of Stevia rebaudiana and noncompetitive inhibition of intestinal contractility by stevioside

Abstract

Stevia rebaudiana (Asteraceae) is a shrub native from Paraguay whose leaves are used as sweetener due to the presence of stevioside and others. It has also hypoglycemic, hypotensor and diuretic effects. This work studied the effects of both, an aqueous crude extract of Stevia rebaudiana (A.c.e) and the stevioside (Stv) in isolated rat thin intestine, and the effects of A.c.e in mice on the open-field-test. The A.c.e of Stevia rebaudiana reduced the spontaneous locomotion and exploration of mice, at doses between 40 to 975 mg lyophilized/ Kg. In the isolated ileons and duodenums, the A.c.e induced a synergism of the acetylcholine doseresponse curve (ACh-DRC) at 0.1-0.3 mg lyophilized/mL and a non-competitive inhibition at higher concentrations (IC50: 1.22±0.16 mg lyoph/ml, n=6). Stv also non-competitively inhibited the ACh-DRC (IC50: 0.84 ± 0.22 mg/ml). Both, A.c.e and Stv inhibited the Ca2+-DRC in 40 mM K+-media in non-competitive way with IC50 of 1.01 ± 0.13 and 1.73 ± 0.47 mg/mL, respectively. Results suggest that Stevia extract exhibited sedative effect and important antispasmodic effect due to non-competitive antagonism of acetylcholine and Ca2+-influx to smooth muscle.