Time course of changes in plasma renin after blockade of the renin-system. Studies of conscious and anaesthetized, normal, adrenalectomized and spontaneously hypertensive rats.

Inhibition of the angiotensin I converting enzyme with SQ 20.881 results in a 2 to 35 fold increase in plasma renin concentration in normal rats and in spontaneously hypertensive rats. The effect is transient, lasting for 1 to 3 hours even in the presence of prolonged blockade. The relative increase is independent of the pretreatment plasma renin concentration. The blood pressure is unchanged in conscious rats in which the effect of SQ 20.881 on plasma renin is believed to be due to a blockade of the negative feedback of angiotensin II on renin release. In anaesthetized rats, SQ 20.88) has an additional hypotensive effect which augments the increase in plasma renin. Saralasin is without effect on blood pressure and plasma renin in conscious normal rats and in spontaneously hypertensive rats, while it causes a transient 3 to 27 fold increase in plasma renin concentration in anaesthetized rats. It is suggested that this increase is hardly due to an interception of the feedback, but to the concomitant fall in blood pressure, as a similar hypotension and increase in plasma renin is produced by dihydralazine. It is furthermore found that Saralasin blocks renin release induced by SQ 20.881. This demonstrates that Saralasin is bound to the receptors in the juxtaglomerular cells and has slight, agonistic properties there. Both in conscious rats and in anaesthetized adrenalectomized rats substituted with DOCA and salt, SQ 20.881 as well Saralasin causes transient increases in plasma renin concentration. If such rats are only substituted with salt and not with DOCA, the effects of both blockers are in the form of severe hypotension and a permanent elevation of plasma renin.