title: Reversal of sodium pump inhibitor induced vascular smooth muscle contraction with digibind. Stoichiometry and its implications.
abstract: The possibility that a circulating sodium pump inhibitor contributes to the pathogenesis of volume-dependent hypertension via an action on vascular smooth muscle (VSM) is supported by multiple lines of investigation, but remains controversial. We had two goals in this study. The first was to compare the pattern of contractile response of rabbit aorta induced by two candidates, ouabain and a labile sodium pump inhibitor that we have identified in the peritoneal dialysate of volume-expanded hypertensive patients with chronic renal failure. Our second goal was to examine the ability of Digibind, a Fab fragment of antisera directed against digoxin, to reverse VSM contraction induced by both agents. Ouabain induced a concentration-dependent contraction, which was delayed in onset, was gradual, and reached a stable plateau after many hours. The labile sodium pump inhibitor induced a qualitatively similar series of responses. Digibind rapidly reversed the contractile responses to both sodium pump inhibitors, with a rate of relaxation that matched that induced by physical removal of the pump inhibitor from the bath. For ouabain, the Digibind:ouabain stoichiometry was highly predictable. When Digibind was present in a molar concentration equivalent to that of ouabain, or less, it had no effect. When the Digibind concentration was twice that of ouabain, complete relaxation occurred. Although the concentration:VSM response relationship for ouabain was steep, the concentration:effect interaction with Digibind was even more steep. The molar concentration of Digibind required to reverse the effects of the labile endogenous inhibitor from peritoneal dialysate was consistently lower than that for ouabain, which is compatible with either greater potency of the labile factor in VSM or greater affinity for Digibind. These findings are compatible with a role for one or more endogenous sodium pump inhibitors as the determinant of vascular smooth muscle tone in the volume-sensitive hypertension of renal disease.
authors.affiliation: Department of Medicine, Harvard Medical School and Brigham and Women's Hospital, Boston, Massachusetts, USA.
authors.forename: H H
authors.initials: HH
authors.lastname: Krep
authors.forename: S W
authors.initials: SW
authors.lastname: Graves
authors.forename: D A
authors.initials: DA
authors.lastname: Price
authors.forename: M
authors.initials: M
authors.lastname: Lazarus
authors.forename: A
authors.initials: A
authors.lastname: Ensign
authors.forename: P A
authors.initials: PA
authors.lastname: Soszynski
authors.forename: N K
authors.initials: NK
authors.lastname: Hollenberg
mesh_terms: D000818:Animals; D001011:Aorta / Q000187:drug effects / Q000502:physiology; D004077:Digoxin / Q000276:immunology; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005260:Female; D006801:Humans; D006973:Hypertension / Q000503:physiopathology*; D007140:Immunoglobulin Fab Fragments / Q000494:pharmacology; D066298:In Vitro Techniques; D009119:Muscle Contraction / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000502:physiology*; D010042:Ouabain / Q000494:pharmacology*; D011817:Rabbits; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors*
chemical_list: D004791:Enzyme Inhibitors; D007140:Immunoglobulin Fab Fragments; C050199:digoxin antibodies Fab fragments; D010042:Ouabain; D004077:Digoxin; D000254:Sodium-Potassium-Exchanging ATPase