Background-Digitalis-like sodium pump ligands (SPLs) effect natriuresis via inhibition of renal tubular Na ϩ ,K ϩ -ATPase but may induce vasoconstriction. The present study investigated the potential roles of 2 putative endogenous SPLs, an ouabain-like compound (OLC) and an ␣ 1 Na ϩ ,K ϩ -ATPase inhibitor, marinobufagenin (MBG), in regulating natriuresis and blood pressure (BP) responses to sustained and acute NaCl loading in Dahl salt-sensitive rats (DS). Methods and Results-During 4 weeks of an 8% NaCl diet, DS exhibited a progressive increase in MBG renal excretion (66Ϯ13 pmol/24 hours at week 4 versus 11Ϯ1 pmol/24 hours at baseline, nϭ48), which paralleled an increase in systolic BP (174Ϯ10 mm Hg at week 4 versus 110Ϯ2 mm Hg at baseline). By contrast, OLC excretion peaked at week 1 and returned to baseline levels. Administration of an anti-MBG, but not anti-ouabain antibody, to DS after 3 weeks of a high NaCl diet lowered BP (139Ϯ7 versus 175Ϯ5 mm Hg, PϽ0.001, nϭ5). Acute NaCl loading (2 hours) of DS (nϭ5) increased MBG and OLC excretion and natriuresis. Pretreatment of acutely NaCl-loaded DS with an anti-MBG antibody (nϭ5) reduced the excretion of sodium and MBG but not that of OLC. An anti-ouabain antibody (nϭ5) reduced sodium excretion and both OLC and MBG. Key Words: hypertension Ⅲ Na ϩ -K ϩ -exchanging ATPase Ⅲ sodium Ⅲ bufadienolides Ⅲ ouabain T he role of endogenous digitalis-like sodium pump ligands (SPLs) in the pathogenesis of hypertension has been disputed for almost 3 decades. 1 Endogenous SPLs are believed to promote natriuresis via renal Na ϩ pump inhibition and may link the Na ϩ retention that occurs during NaCl loading to an increase in arterial pressure via inhibition of the Na ϩ ,K ϩ -ATPase in cardiovascular tissues. [2][3][4] An endogenous ouabain-like compound (OLC) was the first mammalian SPL to be purified. 5 Subsequent studies showed that mammals also produce another class of SPLs, ie, bufadienolides. 6 -8 Bufadienolides, which were discovered in Amphibia, inhibit Na ϩ ,K ϩ -ATPase and cross-react with digitalis antibodies. 9 In Amphibia, skin bufadienolides are responsible for Na ϩ excretion, 9 and bufadienolide levels in toads vary with changes in environmental salinity. 10 Several bufadienolides have been suggested as candidate SPLs in mammals, including marinobufagenin (MBG), 7 which acts in vitro as a vasoconstrictor 11,12 and exhibits greater affinity to rodent ouabain-resistant ␣ 1 isoform of the Na ϩ ,K ϩ -ATPase than to an ␣ 3 isoform. 11,13,14 MBG immunoreactive material purified from human and rat urine was found to be identical to MBG from the toad, Bufo marinus, by mass spectral analysis 15 and by its ability to inhibit rat kidney Na ϩ ,K ϩ -ATPase. 14 Enhanced MBG production occurs in volume-expanded dogs 16 and rats 17 and in pathological states associated with fluid retention, including preeclampsia, 12 hypertension in endstage renal disease, 18 and salt-sensitive hypertension in Dahl rats. 14 In NaCl-induced hypertension in Dahl salt-sensitive rats (DS), which exhibit...

Background Levels of marinobufagenin (MBG), an endogenous bufadienolide Na/K-ATPase (NKA) inhibitor, increase in preeclampsia and in NaCl-sensitive hypertension. Methods We tested a 3E9 monoclonal anti-MBG antibody (mAb) for the ability to lower blood pressure (BP) in NaCl-sensitive hypertension and to reverse the preeclampsia-induced inhibition of erythrocyte NKA. Measurements of MBG were performed via immunoassay based on 4G4 anti-MBG mAb. Results In hypertensive Dahl-S rats, an intraperitoneal administration of 50 μg/kg 3E9 mAb lowered BP by 40 mmHg and activated Na/K-pump in thoracic aorta by 51%. NaCl supplementation of pregnant rats (n = 16) produced a 37 mmHg increase in BP, a 3.5-fold rise in MBG excretion, and a 25% inhibition of the Na/K-pump in the thoracic aorta, compared with pregnant rats on a normal NaCl intake. In eight pregnant hypertensive rats, 3E9 mAb reduced the BP (25 mmHg) and restored the vascular Na/K-pump. In 14 patients with preeclampsia (mean BP, 126 ± 3 mmHg; 26.9 ± 1.4 years; gestational age, 37 ± 0.8 weeks), plasma MBG was increased three-fold and erythrocyte NKA was inhibited compared with that of 12 normotensive pregnant women (mean BP, 71 W 3 mmHg)(1.5 ± 0.1 vs. 3.1 ± 0.2 μmol Pi/ml/h, respectively; P < .01). Ex-vivo 3E9 mAb restored NKA activity in erythrocytes from patients with preeclampsia. As compared with 3E9 mAb, Digibind, an affinity-purified antidigoxin antibody, was less active with respect to lowering BP in both hypertensive models and to restoration of NKA from erythrocytes from patients with preeclampsia. Conclusion Anti-MBG mAbs may be a useful tool in the studies of MBG in vitro and in vivo and may offer treatment of preeclampsia.

These observations provide evidence that MBG contributes to BP elevation in pregnant rats rendered hypertensive by NaCl supplementation.