The effects of saralasin, an angiotensin II antagonist, on blood pressure and the renin-angiotensin-aldosterone system in normal and hypertensive subjects

Comparative study of an angiotensin-II analog and a converting enzyme inhibitor

The effects of an angiotensin-II analog (saralasin, i.v.) and of a converting enzyme inhibitor (captopril, oral) were compared in 12 sodium-depleted patients with hypertension. The decrease of the mean intraarterial pressure (MAP) with captopril (-21.5 +/- [SEM] 4.3 mm Hg) was more pronounced (P < 0.001) than the change of MAP during saralasin (-10.5 +/- 4.0 mm Hg). The pretreatment arterial plasma renin activity (log PRA) was closely related to the change of MAP during saralasin (r = -0.94; P < 0.001) and also to the captopril-induced change of MAP (r = -0.82; P < 0.001); similar results were obtained for the log plasma angiotensin (PA) I and II levels. The change of MAP was more pronounced, however, with captopril than during saralasin at any level of pretreatment PRA, PAI or PAII. Saralasin did not affect heart rate (P > 0.4), but during captopril the heart rate increased by 5.1 beats/min (P < 0.001). Captopril produced a 70% decrease of PAII, but the change of MAP was poorly related to the changes of PAII (r = -0.57; P < 0.05); PRA and PAI rose threefold to fourfold. PRA, PAI, and PAII all increased during saralasin. These observations may suggest that the antihypertensive action of captopril is not based solely on the inhibition of AII formation, but also the agonistic effect of saralasin has to be considered.

Effect of the angiotensin II antagonist saralasin on plasma aldosterone concentration and on blood pressure before and during sodium depletion in normal subjects

The effect of the angiotensin II antagonist saralasin on plasma aldosterone, plasma angiotensin II and blood pressure was studied in six normal supine subjects both before and during sodium depletion. Before sodium depletion, infusion of saralasin produced no consistent changes; during sodium depletion, infusion of the angiotensin antagonist caused a fall in plasma aldosterone and an increase in plasma angiotensin II in each subject. It is concluded that angiotensin II plays a major part in stimulating aldosterone secretion during sodium depletion in man.

Inhibitors of the renin-angiotensin system in experimental hypertension, with a note on the measurement of angiotensin I, II and III during infusion of converting-enzyme inhibitor

1 Prolonged infusion (11 h) of both saralasin and angiotensin-converting enzyme inhibitor (SQ20881) gradually lowered BP in two-kidney hypertensive rats to levels similar to that in normotensive rats infused with dextrose. 2 Saralasin did not lower BP in DOCA-salt hypertensive rats. 3 These observations support the notion that in chronic renal hypertension, angiotensin II may maintain hypertension by a slowly developing action. 4 Plasma angiotensin II in rats infused with SQ20881 was suppressed relative to renin, but was not eliminated. 5 Chromatography of angiotensin II extracts from dogs infused with converting enzyme inhibitor (SQ14,225) showed that the very high levels of angiotensin I achieved after treatment with SQ14,225 can lead to falsely high estimated angiotensin II levels as a result of angiotensin I cross-reacting with the angiotensin II assay.

Correction of renal hypertension in the rat by prolonged infusion of angiotensin inhibitors

Injection of saralasin or converting-enzyme inhibitor produced a small variable reduction of blood-pressure in rats with two-kidney hypertension. Prolonged infusion of the inhibitors gradually reduced blood-pressure to normal. Control infusions of saralasin in normal animals and of dextrose in normal and hypertensive animals did not reduce blood-pressure. Plasma-renin concentration correlated significantly with the early but not with the later fall of blood-pressure. Plasma-concentrations of renin and angiotensin II were closely related except in rats receiving converting-enzyme inhibitor, when angiotensin II was relatively reduced. The gradual reduction of arterial pressure by saralasin was not associated with increased urinary sodium excretion.