1. The influence of single-dose intravenous ouabain on haemodynamics, renal function and vasoactive hormones was investigated in healthy subjects.
2. After ouabain injection there was a significant reduction in minimum and average hourly heart rates. Diastolic blood pressure fell immediately after ouabain, without a significant change in systolic blood pressure.
3. There was no change in renal blood flow, glomerular filtration rate, hourly urine volume or sodium and potassium excretion.
4. Ouabain injection was associated with a fall in plasma angiotensin II levels and a rise in plasma adrenaline levels, but plasma noradrenaline levels were unchanged. Both plasma atrial and brain natriuretic peptide levels were increased after ouabain administration.
5. The present study demonstrates that ouabain has significant although minor, acute effects on plasma levels of vasoactive hormones. It fails, however, to confirm that ouabain is an acute pressor or natriuretic substance. If it has an important influence on electrolyte and haemodynamic homoeostasis, its actions are likely to be slowly developed.