Effect of opioid μ-receptor blockade on rhodiola-water extract-induced plasma glucose lowering action in STZ-diabetic rats. The antagonist was given by an intravenous (i.v.) injection at 30 min before the injection of rhodiola-water extract. Vehicle (0.9% NaCl in distilled water) was given at same volume. Values (mean ± S.E.M.) were obtained from each group of 8 rats. **, p < 0.01 and ***, p < 0.001 compared with data from vehicle-treated STZ-diabetic rats. ##, p < 0.01 and ###, p < 0.001 compared with data from rhodiola-water extract (75 mg/kg)-treated STZ-diabetic rats.