Marinobufagenin, an endogenous alpha-1 sodium pump ligand, in hypertensive Dahl salt-sensitive rats.
Dahl salt-sensitive rats (DS), which have a mutation in the alpha-1 subunit of Na(+)/K(+)-ATPase, exhibit impaired pressure natriuresis and on a high-salt diet, retain Na(+) and exhibit increased blood pressure. Recently, we have shown that mammalian tissues contain a bufadienolide Na(+)/K(+)-ATPase inhibitory factor, marinobufagenin (MBG), that exhibits greater affinity for the alpha-1 than alpha-3 sodium pump isoform. The present study investigated the possible role of MBG in hypertension in DS on a high NaCl intake. Eight DS and 8 Dahl salt-resistant rats (DR) were placed on an 8% NaCl diet. Within 2 weeks, systolic blood pressure increased in DS (162+/-9 mm Hg at week 2 versus 110+/-2 mm Hg in baseline, P<0.01), and increased less in DR (124+/-3 mm Hg at week 2 versus 112+/-2 mm Hg in baseline). Renal excretion of MBG increased 4-fold (38.9+/-7.6 pmol versus 9.1+/-1.3 pmol in baseline, P<0.01) in DS, but by only 25% in DR (13.2+/-0.9 pmol versus 10.3+/-0.7 pmol in baseline). Excretion of endogenous ouabain did not change in either strain. MBG-immunoreactive material was purified from the urine of hypertensive DS by means of 2 steps of reverse-phase high performance liquid chromatography (HPLC) and compared with plant ouabain and amphibian MBG for its ability to inhibit the Na(+)/K(+)-ATPase from rat kidney (which expresses only alpha-1 Na(+)/K(+)-ATPase isoform). Unlike ouabain (IC(50)=248 micromol/L), serially diluted, HPLC-purified MBG immunoreactivity from DS and authentic MBG potently inhibited rat kidney Na(+)/K(+)-ATPase (IC(50)=70 and 78 nmol/L, respectively). Our results suggest that an alpha-1 Na(+)/K(+)-ATPase ligand, MBG, is elaborated to promote natriuresis in hypertensive DS. MBG acts as a selective inhibitor of the ouabain-resistant alpha-1 Na(+)/K(+)-ATPase subunit, ie, the major sodium pump isoform of the kidneys, as would be expected of a putative natriuretic hormone.
Fedorova
O V
OV
Laboratory of Cardiovascular Science, Intramural Research Program, National Institute on Aging, Baltimore, Md, USA.
Kolodkin
N I
NI
Agalakova
N I
NI
Lakatta
E G
EG
Bagrov
A Y
AY
D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D002018:Bufanolides / Q000097:blood / Q000302:isolation & purification / Q000378:metabolism* / Q000652:urine; D002851:Chromatography, High Pressure Liquid; D004791:Enzyme Inhibitors / Q000378:metabolism; D006973:Hypertension / Q000097:blood / Q000378:metabolism* / Q000652:urine; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000302:isolation & purification; D007668:Kidney / Q000201:enzymology*; D009318:Natriuresis; D010042:Ouabain / Q000097:blood / Q000652:urine; D051381:Rats; D020303:Rats, Inbred Dahl; D012964:Sodium / Q000097:blood; D012965:Sodium Chloride / Q000008:administration & dosage; D012982:Sodium, Dietary / Q000008:administration & dosage; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors* / Q000302:isolation & purification
D002018:Bufanolides; D004791:Enzyme Inhibitors; D007527:Isoenzymes; D012982:Sodium, Dietary; C093896:marinobufagenin; D012965:Sodium Chloride; D010042:Ouabain; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase