Effect of captopril on changes in plasma noradrenaline induced by sodium nitroprusside

There is much animal data to suggest that angiotensin II has a regulatory role in noradrenaline release. We sought evidence for such a mechanism in man by pretreating six normal volunteers with captopril (50 mg) or placebo and then infusing them with incremental doses of sodium nitroprusside. Pretreatment with captopril had no significant effect on the mean arterial pressure, heart rate or plasma noradrenaline response to sodium nitroprusside, despite increasing plasma renin activity. This suggests that in normotensive salt replete man, normal levels of angiotensin II do not exert any tonic effect on noradrenaline release.