COMPARISON OF THE EFFECTS OF OUABAIN AND BRAIN NATRIURETIC PEPTIDE INSALINE-LOADED SHEEP

1. It has been claimed that ouabain is an endogenous hormone that may be pivotal in the pathogenesis of some forms of hypertension and may e xaggerate natriuresis in situations characterized by volume overload, We compared the haemodynamic, renal and endocrine effects of ouabain ( at approximately 187 ng/kg per min for 2 h) with those of brain natriu retic peptide (BNP; at 5 pmol/kg per min for 2 h) in nine saline-loade d sheep in a balanced, randomized, single-blind, placebo-controlled cr ossover study. 2. Brain natriuretic peptide infusion reduced mean arte rial pressure whereas ouabain infusion caused no change, Haematocrit r ose steadily during BNP infusion but fell during ouabain infusion, Nei ther ouabain nor BNP affected urine volume, sodium, potassium or creat inine excretion, Mean heart rate declined during the ouabain and place bo infusions, but was not altered during BNP infusion, Endogenous ouab ain concentrations were not detectable at baseline or during BNP or pl acebo infusions, but rose to concentrations of 11+/-1.3 nmol/L during the ouabain infusion. 3. These results suggest that ouabain is not an endogenous hormone present at physiologically relevant concentrations, Furthermore, ouabain does not cause natriuresis during saline-loading in sheep and is therefore unlikely to be responsible for the exaggera ted natriuresis seen in some forms of hypertension.