Effects of digoxin-specific antibody Fab fragment (Digibind) on blood pressure and renal water–sodium metabolism in 5/6 reduced renal mass hypertensive rats

The importance of increased endogenous digitalis-like factor (EDLF) in volume-expanded hypertension has been generally agreed. To further clarify the role of EDLF on the development of hypertension and renal water-sodium handling in 5/6 reduced renal mass hypertensive rats (RRM), we studied the effects of acute administration of digoxin-specific antibody Fab fragment (Digibind) in the early phase and the chronic phase of hypertension in RRM. RRM and sham-operated rats were given 1% saline for 1 or 4 weeks. RRM were injected Digibind (60 mg/kg) or vehicle (0.9% saline) intravenously in the first or fourth week under thiobutabarbital anesthesia. All sham-operated rats were administered Digibind under the same condition. Digibind altered neither blood pressure, heart rate, urine volume, nor urinary sodium excretion in sham-operated rats. However, Digibind produced a gradual but significant decline in mean arterial pressure to the level slightly above that in sham-operated rats from 153 ± 5 to 131 ± 5 mm Hg in the first week and from 181 ± 6 to 129 ± 4 mm Hg in the fourth week without any significant change in heart rate. The decrease in mean arterial pressure at 160 min after Digibind administration in the fourth week (−48 ± 5 mm Hg) was greater than that in the first week (−22 ± 4 mm Hg). No differences were observed in urine volume, urinary sodium excretion, or plasma norepinephrine concentration between Digibind and vehicle-treated RRM in either week. These data suggest that EDLF would contribute to both the early and chronic phase in the development of hypertension in RRM.