Spironolactone inhibits vascular reactivity by a prostaglandin related mechanism unconnected with aldosterone

Effects of aldosterone and spironolactone on the vascular responses to noradrenaline and potassium were studied in the perfused rat mesenteric vascular bed. Aldosterone did not modify the response to either vascular agent. Spironolactone inhibited the vascular response to both pressor agents in a dose-dependent manner. The inhibitory effect of spironolactone was not altered by various concentrations of aldosterone and ouabain. However it was not apparent in preparations in which endogenous prostaglandin synthesis had been abolished in indomethacin. The observations suggest that spironolactone has actions on vascular reactivity which are not related to aldosterone or to sodium/potassium pumping. They may depend on modification of prostaglandin biosynthesis.