Ouabain-Like Compound Changes Rapidly on Physical Exercise in Humans and Dogs Effects of -Blockade and Angiotensin-Converting Enzyme Inhibition

Ouabain, an inhibitor of the sodium pump, has been identified as a constituent of bovine adrenal glands. We were interested whether the release of this cardiotonic steroid is stimulated by physical exercise. Hence, athletes and healthy dogs were subjected to ergometry. Ouabain-like compound (OLC) was measured in venous blood by enzyme-linked immunosorbent assay as well as by Rb uptake inhibition (as ouabain equivalents). OLC increased in venous blood of athletes after 15 minutes of ergometry from 2.5 0.5 to 86.0 27.2 nmol/L (n 51; P 0.001), as did the concentration of a circulating inhibitor of the sodium pump from 7.3 1.7 to 129.8 51 nmol/L (ouabain equivalents, P 0.05). Half-maximal increase in heart rate and systolic blood pressure occurred at 5.1 1.2 nmol/L and at 30 1 nmol/L OLC, respectively. On rest, OLC decreased in humans and dogs with a half-life of 3 to 5 minutes. In beagles exposed to moderate exercise on a treadmill for 13 minutes, levels of OLC increased 46-fold (from 3.7 0.8 to 166.9 91.8 nmol/L; n 6; P 0.005). This effect was suppressed when the dogs had been treated for 3 weeks with the 1-adrenergic receptor blocker atenolol or the angiotensin-converting enzyme inhibitor benazepril. We conclude that OLC changes rapidly during exercise and is under the control of norepinephrine and angiotensin II. (Hypertension. 2005;45:1024-1028.)