CHRONIC OUABAIN INFUSION DOES NOT CAUSE HYPERTENSION IN SHEEP

Ouabain is claimed to be a hormone of adrenal origin, capable of raisi ng arterial pressure in rats. We infused ouabain in conscious sheep un der carefully controlled circumstances to determine its effects on blo od pressure, urine electrolytes, and vasoactive hormones. Eight health y ewes were studied while taking a constant intake of dietary sodium a nd potassium. Ouabain infusion at 0.25 mg daily over 22 days reduced h eart rate and arterial pressure and had no effect on presser responsiv eness to incremental intravenous infusions of angiotensin II. Ouabain induced minor, but statistically significant, decrements in urine volu me, urinary sodium excretion, plasma renin and angiotensin II concentr ations, and a rise in plasma aldosterone and cortisol. Plasma ouabain levels averaged 1.37 +/- 0.28 nmol/l during ouabain infusion. In concl usion, high-dose chronic ouabain infusion in sheep did not elevate art erial pressure or alter presser responsiveness to angiotensin II, was antidiuretic and antinatriuretic, and induced minor perturbations in c irculating renin, angiotensin II, aldosterone, and cortisol.