Compared effects of indapamide, hydrochlorothiazide and chlorthalidone on electrical and mechanical activities in vascular smooth muscle.

The effects of indapamide, hydrochlorothiazide and chlorthalidone were studied on isometric contractions, calcium contractures (in depolarized preparations) and membrane potentials in isolated longitudinal strips from rat portal veins. Indapamide inhibited all three responses more potently than did current diuretics. The effects of hydrochlorothiazide and chlorthalidone appeared at concentrations at which indapamide reduced electrical and mechanical activity by more than 50%. These results confirmed that the depressing action of indapamide on vascular smooth muscle was exerted through a reduction in the transmembrane calcium influx.