Effect of spironolactone on systemic blood pressure, limb blood flow and response to sympathetic stimulation in hypertensive patients
Since there is only scanty, indirect information about the mechanism of the hypotensive effect of spironolactone, 9 patients with essential hypertension were studied according to a randomised double-blind, cross-over protocol. Spironolactone 100mg b.i.d. and placebo were each given for one month and the following parameters were studied: blood pressure, heart rate, response to cold pressure and hand-grip tests, as well as blood flow in the calf and finger vessels. Flow in the calf and fingers representing muscle and skin arteries, respectively, was measured semicontinuously with an ECG-triggered venous occlusion plethysmograph. After spironolactone there was a significant decrease in the systolic and diastolic blood pressures in the supine, sitting and standing positions; the sitting systolic and diastolic blood pressure decreased by (mean ± SE) 27±4mm Hg (p<0.001) and 11±4mm Hg (p<0.02), respectively. No orthostatic response was observed. Heart rate remained unchanged. Blood flow through muscle and skin vessels increased in 6 out of 9 patients, and in these patients calculated vascular resistance in these areas decreased. Spironolactone did not significantly change the response of systemic blood pressure to the handgrip and cold pressure tests. The present data confirm the hypotensive properties of spironolactone and show that this effect is associated with dilatation of muscle and skin arteries in many but not in all the patients. The data do not support the hypothesis that spironolactone decreases the responsiveness of systemic blood pressure to orthosympathetic stimulation.