Volume sensitive hypertension and the digoxin-like factor reversal by a fab directed against digoxin in DOCA-salt hypertensive rats

Although volume and vasoconstriction have been considered polar elements in a useful pathogenetic hypertension model, many observations suggest that vasoconstriction is involved in volume-dependent hypertension, reflecting the effect of a digitalis-like factor. To examine that possibility, we assessed the depressor responses to Digibind, an antibody Fab directed against digoxin, in a volume-dependent model-DOCA-salt-induced hypertension in rats. Digibind (10 mg/kg, intravenously) induced a gradual blood pressure fall over 2 h that was sustained for 4 h (P< .001). Blood pressure did not fall with Digibind when DOCA was administered without salt or a high-salt intake was provided without DOCA. The intracellular sodium content of the rat aorta, measured by atomic absorption spectroscopy after cold choline wash, was increased in the DOCA-high-salt rats (23.3 ± 2.7 mEq/L) compared to control rats (12.1 ± 0.8 mEq/L; P< .001. Aorta sodium content, in parallel with blood pressure, was not increased either by dietary salt supplementation without DOCA, or by DOCA with a low-salt diet. Sodium pump activity was measured as 86Rb uptake into vascular smooth muscle (VSM). Both ouabain-sensitive and ouabain-resistant 86Rb uptake were significantly higher in VSM from DOCA-high-salt animals (P< .01). Despite its effectiveness in reducing blood pressure in this model, Digibind influenced neither VSM sodium content nor 86Rb uptake. The results are consistent with a role for a circulating digitalis-like factor in this volume-dependent model, but events at the VSM level are complex.