Influence of calcium on the blood pressure and renal effects of stevioside.

1. The effects of verapamil (V, 0.015 mg/min, i.v.) or CaCl2 (800 mEq/l, 0.025 ml kg-1 min-1, i.v.) on renal function and mean arterial pressure (MAP) were evaluated in male Wistar rats weighing 280-320 g during treatment with stevioside (S, 16 mg kg-1 h-1, i.v.). 2. Verapamil administered to 10 rats significantly increased the hypotensive effect of stevioside on MAP (control, 124 +/- 0.77; S, 96 +/- 1.50; S+V, 67 +/- 0.70 mmHg) and on fractional sodium excretion (control, 0.76 +/- 0.05; S, 1.56 +/- 0.10; S+V, 2.72 +/- 0.25%). Urinary flow, reported as percent glomerular filtration rate (V/GFR), and renal plasma flow (RPF) increased slightly but not significantly during stevioside plus verapamil administration. 3. In contrast, infusion of CaCl2 in 10 rats pretreated with stevioside induced a marked attenuation of MAP (control, 119 +/- 1.83; S, 70 +/- 1.12; S+CaCl2, 109 +/- 1.60 mmHg) and RPF (control, 16.73 +/- 3.76; S, 34.33 +/- 2.55; S+CaCl2, 17.20 +/- 2.87 ml min-1 kg-1). The diuresis and natriuresis induced by stevioside were also inhibited by simultaneous administration of CaCl2. 4. These data are consistent with the view that stevioside acts on arterial pressure and renal function as a calcium antagonist, as is the case for verapamil.