(Hypertension. 1996;27:1073-1078.)
© 1996 American Heart Association, Inc.
Articles |
Pulse Pressure Correlates in Humans With a Proscillaridin A Immunoreactive Compound
From the Institut für Biochemie und Endokrinologie, Justus-Liebig-Universität Giessen (B.S., U.K., W.S.), and Medizinische Poliklinik Münster, Westfälische Wilhelms-Universität Münster (M.T., W.Z.) (Germany).
 |
Abstract |
|---|
 Top Abstract IntroductionMethodsResultsDiscussionReferences |
|---|
Abstract Endogenous digitalis-like factors in humans are presumably cardenolides and bufadienolides. To test whether bufadienolide-like substances may circulate in human blood, we used antibodies from rabbits against the bufadienolide proscillaridin A to measure the concentration of cross-reacting material in human plasma with an indirect enzyme-linked immunosorbent assay. IgG had an apparent affinity of 2x10-9 mol/L for proscillaridin A. It was specific for bufadienolides and did not cross-react with cardenolides or several steroid hormones. Extraction of human plasma with ethanol and fractionation of this extract over a high-performance liquid chromatographic reverse-phase C18 column with a propanol/isopropanol gradient resulted in the separation of three peaks of increasing hydrophobicity (ED1, ED2, ED3) that inhibited the sodium pump of human red blood cells and cross-reacted with proscillaridin A antibodies. The concentration of the proscillaridin A immunoreactivity ED1 in normotensive subjects had a geometric mean of 0.1 nmol/L, with a dispersion factor of 8.77. ED1 correlated positively in a group of 60 normotensive subjects, 22 patients with hypertension, and 19 patients with chronic renal failure with mean arterial blood pressure (log ED1 [nmol/L]=0.013xmm Hg-2.17, r=.25, P<.05), systolic pressure (log ED1 [nmol/L]=0.010xmm Hg-2.23, r=.32, P<.01), and pulse pressure (log ED1 [nmol/L]=0.019xmm Hg-1.80, r=.38, P<.0001). There was no correlation with other parameters of the donors. We conclude that several substances cross-reacting with proscillaridin A antibodies and inhibiting the sodium pump of human red blood cells circulate in human blood. The level of one of these substances (ED1) correlates with mean arterial and pulse pressures.
Key Words: proscillaridin A • hypertension, essential • blood pressure • bufanolides • immunoassay • pulse pressure • Na+-K+-exchanging ATPase
|
Introduction |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
Endogenous compounds with digitalis-like action are considered to circulate in increased concentrations in blood in essential hypertension and various conditions of volume expansion.1 2 3 4 The search for such compounds has revealed that ouabain or a ouabain isomer5 is produced by the adrenal cortex6 and is elevated in hypertension.4 7 A ouabain isomer is also found in the hypothalamus.8 A substance indistinguishable from digoxin has been isolated from human urine.9 A substance not identical with digoxin but cross-reacting with digoxin antibodies has been shown to exist in adrenals.10 It is well documented that a material cross-reacting with digoxin antibodies is available in increased concentrations in umbilical cord blood.11 Recently, 19-norbufalin has been isolated from human cataract lenses.12 An endogenous marinobufagenin-like immunoreactive factor circulating in blood and inhibiting the sodium pump has been found to increase with pressure response as the result of hypoventilatory breathing.13 Since toads are vertebrates and synthesize several bufadienolides in their skin,4 it seemed possible that other vertebrates, such as humans, may also be able to synthesize several bufadienolide-like compounds. Therefore, we raised antibodies against the bufadienolide proscillaridin A in rabbits and assayed its concentration in human plasma. This report shows that a material cross-reacting with antibodies against a bufadienolide circulates in blood and correlates with systolic and mean arterial BP values as well as pulse pressure.
|
Methods |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
Materials
Gelatin was obtained from Bio-Rad, heptafluorobutyric acid from Pierce Chemical Co, and the silicon oils AR 200 and AR 20 from Wacker Chemie. N-Acetylglucosaminyl-(ß1-4)-N-acetylmuramyl-L-alanyl-D-isoglutamin (GMDP) was from Gerbu Biotechnik, the protein A column MemSep 1010 from Millipore, 86RbCl from Amersham/Buchler, and biotinylated goat anti-rabbit IgG as well as streptavidin conjugated to alkaline phosphatase from Jackson ImmunoResearch Dianova. All other chemicals were of the highest purity available and were obtained from Merck, Sigma Chemical Co, Roth, Boehringer, and Serva. Marinobufagenin was a kind gift from Dr A.Y. Bagrov, Laboratory of Pharmacology, Sechenov Institute of Evolutionary Physiology and Biochemistry, St Petersburg, Russia.
Patients
Plasma for use in this study was obtained from 22 essential
hypertensive patients, 60 normotensive control subjects, and 19
patients with chronic renal failure. The characteristics of the
patients are given in Table 1
. Patients were randomly
recruited from among outpatients. All were free of major medical
illness and did not have significant pain, elevated temperature, or any
acute condition. Individuals with major medical illness and those who
had taken prescription medications (including antihypertensive
medication, nonsteroidal anti-inflammatory drugs, aspirin, or
cardiac glycosides) were excluded. After subjects had rested for 10
minutes, seated BP measurements were obtained with conventional
sphygmomanometric methods by the same individual. Subjects were
considered normotensive if their BP was less than 140/90 mm Hg. A
diagnosis of hypertension was based on a BP greater than or equal to
160/90 mm Hg or a diastolic BP of 95 mm Hg or higher.
Diagnosis of chronic renal failure was based on serum
creatinine concentration greater than or equal to 106
µmol/L. Chronic renal failure was due to chronic glomerulonephritis
(n=11), interstitial nephritis (n=6), and polycystic kidney
disease (n=2). None of the patients was undergoing hemodialysis.
|
[Nai]P was determined fluorimetrically by use of the sodium-sensitive fluorescent indicator sodium-binding benzofuran isophthalate.14 All other serum values—sodium (Na+), potassium (K+), calcium (Ca2+), glucose, creatinine, uric acid, and urea—were obtained by routine clinical chemical methods.
Production and Purification of Antibodies Against
Proscillaridin A
Specific polyclonal antibodies against the bufadienolide
proscillaridin A were raised in four New Zealand White rabbits.
Proscillaridin A was coupled to bovine serum albumin according
to a procedure similar to the one of Terano et al15 and
Harris et al.16 Proscillaridin A (100 µg) coupled to
bovine serum albumin in 0.5 mL of 0.9% NaCl solution was
emulsified with 0.5 mL Freund's complete adjuvant. This mixture was
injected intradermally at five to six sites along the spinal column.
Booster injections of 100 µg antigen dissolved in 0.5 mL of 0.9%
NaCl solution and also in either 0.5 mL incomplete Freund's adjuvant
or 10 µg GMDP were administered at 4-week intervals as described
above. Rabbits were bled 40 weeks after the start of the immunization
procedure. The globulin fraction of antiserum in 1 mol/L glycine and
0.5 mol/L NaCl (pH 8.9) was applied to a protein A MemSep 1010 column.
IgG was eluted with 0.1 mol/L citric acid (pH 3.0); the pH of the
eluate was adjusted to 7 with Tris base and concentrated by
ultrafiltration. The concentrated IgG fraction was stored in Tris-NaCl
buffer (50 mmol/L Tris, 150 mmol/L NaCl, pH 7.8) containing 0.02%
NaN3 and 50% glycerol at -20°C.
Preparation of Plasma for Measurement of Proscillaridin A
Immunoreactivity by Indirect ELISA and for Detection of Sodium Pump
Inhibition With 86Rb+ Uptake Into Human Red
Blood Cells
The extraction was performed as described
previously.17 The water-soluble extract of 2 mL plasma
after ethanol precipitation was applied to a LiChrospher 250-5 RP18
HPLC column and separated by a propanol/isopropanol gradient in 0.1%
heptafluorobutyric acid according to Hamlyn et al.18 Three
fractions, ED1, ED2, and
ED3, with increasing hydrophobicity were collected
and measured by an indirect competitive ELISA. Each of the
ED1, ED2, and ED3
fractions was dissolved in 500 µL PBS, and volumes between 10 and 100
µL were included in the ELISA test system. All measurement was done
in duplicate. Only those values showing a concentration dependency were
included in this study.
For testing of the ability of the ED1, ED2, and ED3 fractions to inhibit the sodium pump, the residue was taken up in 250 µL distilled water after lyophilization.
Indirect ELISA for Proscillaridin A Immunoreactivity
Microtiter plates were coated with 100 µL antigen per well
(proscillaridin A coupled to gelatin with a variation of the procedures
of References 15 and 1615 16 ) in coating buffer (15 mmol/L
Na2CO3, 35 mmol/L
NaHCO3, pH 9.6) with a concentration of 100 µg/mL
for 1 hour. Free binding sites were blocked with 1% gelatin in PBS for
30 minutes. Thereafter, 10 to 100 µL of the HPLC-purified plasma
sample (0.04 to 0.4 mL plasma equivalents) was added and incubated with
10 µL proscillaridin A–IgG (1:1000 diluted in PBS) for 1 hour. Bound
proscillaridin A–IgG was detected with 100 µL biotinylated goat
anti-rabbit IgG (1:5000 in PBS for 1 hour) and 100 µL alkaline
phosphatase coupled to streptavidin (1:500 in PBS for 30 minutes).
Phosphatase activity was measured by addition of 100 µL
p-nitrophenylphosphate (1 mg/mL) as a substrate in 0.5
mmol/L MgCl2 and 10 mmol/L diethanolamine (pH 9.5). The
phosphatase reaction proceeded for 30 minutes and was stopped by
addition of 50 µL of 3 mol/L NaOH. The yellow
p-nitrophenolate formed was measured by a microtiter
photometer (Multiscan MCC/340) at 405 nm. Between the incubation steps,
washing was performed three times for 3 minutes with 200 µL of 150
mmol/L PBS, pH 7.4 (140 mmol/L NaCl, 3 mmol/L KCl, 1.5 mmol/L
KH2PO4, and 5.5 mmol/L
Na2HPO4).
This assay system was also used for measurement of the serum titer for proscillaridin A antibodies and testing of cross-reactivity of the purified anti–proscillaridin A–IgG with other cardiac glycosides and steroid hormones.
Quantification of Sodium Pump Inhibitor by Measurement
of Ouabain-Sensitive 86Rb+ Uptake Into Human
Red Blood Cells
To examine whether HPLC fractions cross-reacting with
proscillaridin A antibodies inhibit the sodium pump, we tested their
potency to inhibit ouabain-sensitive 86Rb+
uptake into human red blood cells by a procedure described
previously.19 For the quantification of the
inhibitor concentration, it was assumed that the
endogenous inhibitor binds with the same
affinity as ouabain binds to the sodium pump of human red blood cells.
Half-maximal inhibition of the sodium pump of human red blood cells
was seen at 4x10-8 mol/L ouabain.
Concentrations of the HPLC-purified plasma extract giving
half-maximal inhibition were assumed to contain
4x10-8 mol/L inhibitor
units. Half-maximal inhibition was extrapolated after subtraction
of the ouabain-independent 86Rb+ uptake
from all values from a double logarithmic plot (%
inhibition/100-% inhibition) against the concentration of the
inhibitor.19
Statistics
Statistical analysis was done by the BMDP computer
programs20 and GraphPad Prism (GraphPad Software). Because
the statistical distribution of the ED1,
ED2, and ED3 concentrations were nearly
log normal, their values are represented as geometric mean
with dispersion factor. All other data are represented as
mean value and SE. The geometric means of the proscillaridin A
immunoreactivities ED1, ED2, and
ED3 of the three groups of patients (normotensive,
hypertensive, and patients with chronic renal failure) were compared by
the nonparametric Kruskal-Wallis test as well as multiple
comparison (Nemenyi test) using the BMDP-3S program. Regression
analysis of log ED1, log
ED2, and log ED3 was tested as a
function of systolic, diastolic, and mean
arterial BP values as well as of pulse pressure,
[Nai]P, age, body mass index, and
serum concentrations of Na+, K+,
Ca2+, glucose, creatinine, uric acid,
and urea with GraphPad Prism. Mean values of parameters
other than ED1, ED2, and
ED3 were compared in a two-sided Student's
t test or Mann-Whitney test with comparison related
significance level. The two-tailed level of significance was set at
a value of P<.05.
|
Results |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
Development of an Indirect ELISA for Proscillaridin A and Bufadienolide-Like Substances
To develop an immunological assay for the bufadienolide proscillaridin A and bufadienolide-like immunoreactive substances, we immunized rabbits with proscillaridin A coupled to bovine serum albumin. Rabbits produced antibodies with a titer of 1:103 after 40 weeks and a Kd value of 2x10-9 mol/L. This titer and affinity remained constant from the 25th to the 120th week after immunization. When the specificity of the antibodies was tested, only bufadienolides such as proscillaridin A and bufalin were recognized (marinobufagenin was almost not recognized); cardenolides such as ouabain and digoxin or other steroid hormones were not recognized (Table 2
).
With these antibodies, concentrations as low as 100 fmol per well or
10-9 mol/L could be detected. The range
for determinations of proscillaridin A was
10-7 to
10-10 mol/L. The interassay coefficient
of variation of the method was 18.6%, and the intra-assay
coefficient was 8.8%. The curve of proscillaridin A immunoreactivity
as a function of plasma volume was superimposed over the proscillaridin
A standard curve (Fig 1).
|
|
Characterization of Patients
All three groups of patients—normotensive subjects, patients
with hypertension, and patients with chronic renal failure—had
normal and equal serum levels of Na+,
K+, Ca2+, and glucose. Patients
with chronic renal failure had significantly elevated levels of
creatinine (P<.001), uric acid
(P<.05), and urea (P<.001) compared with
normotensive subjects and hypertensive patients (Table 1
). Body mass
index of all groups did not differ. The hypertensive patients had a
significantly higher (P<.05) diastolic BP
compared with normotensive subjects and patients with chronic renal
failure (Table 3). Patients with chronic renal failure
had a significantly (P<.05) higher
[Nai]P compared with normotensive subjects
and hypertensive patients (Table 3).
|
Determination of Proscillaridin A Immunoreactivity in Serum of
Healthy Normotensive Subjects and Patients With Essential Hypertension
and Chronic Renal Failure
Before measurement of immunoreactivity, we separated the ethanolic
extracts by reverse-phase C18 HPLC using a propanol/isopropanol
gradient as described by Hamlyn et al.18 Chromatograms of
the ethanolic plasma extracts are shown in Fig 2. It is
evident that three peaks of proscillaridin A immunoreactive material
with different polarities and retention times were eluted from the C18
reverse-phase column (Fig 2B). These three peaks also inhibited the
cardiac glycoside–sensitive 86Rb+ uptake
into human red blood cells (Fig 2A). The peak with a retention time of
20 minutes and almost the same polarity as ouabain was denoted as
ED1 in all further investigations. In addition, more
hydrophobic fractions with proscillaridin A immunoreactivity were seen.
The peak with a retention time of approximately 40 minutes was called
ED2, and the most lipophilic fraction with a
retention time of 60 minutes and a polarity similar to that of
proscillaridin A was named ED3 (Fig 2).
|
An analysis of the plasma concentrations of proscillaridin A
immunoreactivity of 60 normotensive subjects revealed a
non-gaussian distribution of the individual values. However, it
showed a logarithmic distribution curve like other hormones. Therefore,
geometric means and dispersion factors were calculated for each
fraction of ED1, ED2, and
ED3 proscillaridin A immunoreactivity. When the
concentrations of ED1, ED2, and
ED3 were compared, for all groups of patients,
ED1<ED2<ED3 (Table 3). Although
inspection of the ED1, ED2, and
ED3 values of proscillaridin A immunoreactivity indicates a
tendency for higher values in hypertensive patients compared with
normotensive subjects for the geometric mean (Table 3), statistical
analysis by the Kruskal-Wallis test and Tukey comparison was
unable to detect any significant differences between the patient
groups. However, we cannot exclude the possibility that a higher number
of investigations may reveal such differences.
No correlations were found between the ED2 and
ED3 concentrations of proscillaridin A immunoreactivity and
the individual systolic, diastolic, and mean BP
values of their plasma donors; pulse pressure; body mass index; and age
of the patients. There also was no correlation with
[Nai]P and other plasma concentrations such
as Na+, K+,
Ca2+, glucose, creatinine, uric acid,
and urea. The ED1 values of proscillaridin A
immunoreactivity also did not correlate with these plasma
concentrations, the [Nai]P of their donors,
body mass index, or age. However, the ED1 concentration of
proscillaridin A immunoreactivity showed a significantly positive
correlation with systolic BP (P<.01, Fig 3A), mean BP (P<.05, Fig 3B), and pulse
pressure (P<.0001, Fig 3C), but it did not correlate with
diastolic BP.
|
|
Discussion |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
Increased circulating levels of sodium pump inhibitors have been implicated in the pathogenesis of hypertension.2 19 21 22 The search for sodium pump inhibitors or for substances with endogenous digitalis-like action in human serum has led to the detection of an isomer of the cardenolide ouabain5 6 7 that is twofold to threefold elevated under the conditions of hypertension. Elevated concentrations were also found in patients with adrenocortical tumors, aldosteronism, and heart failure (for a recent review see Reference 2323 ). Evidence is accumulating that the compound is produced in the adrenal cortex and that its release and synthesis are increased by corticotropin and angiotensin II.6 23 Endogenous ouabain, however, does not seem to be the sole compound with cardiac glycoside–like action in serum. Numerous reports show elevated levels of a compound or compounds cross-reacting with digoxin antibodies in hypertension.3 11 This assay system is not digoxin specific because compounds indistinguishable from ouabain have been isolated by affinity chromatography on digoxin antibodies as well.24 However, a compound resembling digoxin in its polarity has been detected in adrenals,10 and a substance that cannot be distinguished from digoxin was isolated from the urine of individuals not receiving any digoxin treatment.3 The body of evidence for the existence of a biosynthetic pathway for the cardenolides in adrenal glands is growing,6 10 and recent reports add the suggestion that bufadienolides may be formed in mammals as well. The bufadienolide 19-norbufalin has been isolated from cataracts in human lenses.12 Recently, Bagrov et al13 reported on the existence of a marinobufagenin-like compound in blood and urine of humans that seems to be related to the rise in BP. This compound is more hydrophobic than ouabain. Interestingly, the hydrophobic bufalin has been shown to raise BP when administered acutely25 and to be a more potent vasopressor agent than ouabain.26 Since toads are vertebrates and synthesize several bufadienolides, we speculated that mammals may be able to synthesize such compounds as well.
The present report shows that in fact several substances
cross-reacting with an antibody against the bufadienolide
proscillaridin A and inhibiting the sodium pump of red blood cells
circulate in human blood (Fig 2). However, only the most polar
substance in the serum with a retention time similar to that of ouabain
correlated with the rise of mean and systolic BP values and
pulse pressure (Fig 3). Since the concentrations of the hydrophilic
ED1 proscillaridin A immunoreactivity did not correlate
with diastolic pressure, this substance does not seem to be
responsible for the increase of peripheral resistance in
hypertensive patients. Although stroke volume is only one determinant
of pulse pressure, the correlation of ED1 levels with pulse
pressure is compatible with the hypothesis that ED1 may
have a positive inotropic effect and thereby affect pulse pressure (Fig 3C). The anti–proscillaridin A–IgG used in the present study
did not cross-react with cardenolides but did cross-react with
a different bufadienolide, bufalin, and slightly with marinobufagenin
(Table 2). It is unlikely, therefore, that ouabain was measured in the
present study despite the similarity in retention times with
authentic ouabain in the HPLC system used to detect
endogenous material cross-reacting with proscillaridin
A antibodies. Although the antibody used in the present study
cross-reacts slightly with marinobufagenin (Table 2), we did not
assay this compound. Marinobufagenin is more hydrophobic than
ouabain13 and elutes with a higher retention time than
ouabain in the HPLC system used for the clean up of proscillaridin A
immunoreactivity. Additionally, the marinobufagenin antibody of Bagrov
et al13 does not cross-react with proscillaridin A,
and the endogenous marinobufagenin shows different
physiological properties.13 Therefore,
it is highly probable that two different inhibitors
of the sodium pump are tested by antibodies against proscillaridin A
and marinobufagenin.
Considering the fact that 19-norbufalin12 and an endogenous marinobufagenin13 exist in humans, it is tempting to speculate that several bufadienolides may circulate in blood. Since bufadienolides show a distinct UV maximal absorbance at 300 nm, it should not be difficult to substantiate this speculation. Preliminary studies with affinity purification of a material from bovine adrenals cross-reacting with proscillaridin A antibodies led to the isolation of a pure compound that failed to show UV absorbance at 300 nm.27 Consequently, it is likely that an inotropic substance other than a bufadienolide may circulate in blood and mimic the action of a bufadienolide by binding to the sodium pump and to antibodies against proscillaridin A.
The geometric mean of the ED1 proscillaridin A immunoreactive material in serum was 0.102 nmol/L (with a dispersion factor of 8.77) in 60 normotensive subjects. Endogenous ouabain in 11 normotensive human volunteers has been found by Harris et al16 to be 0.138±0.043 nmol/L. Evidently, both substances exist in humans in the same concentration range. It is unclear thus far whether the actions of both substances are additive. It is well known that multiple digitalis receptor sites differing in their affinities exist in mammals.28 The physiological meaning of this observation is unknown. It will be interesting to determine whether the various substances with endogenous digitalis-like actions affect specific isoforms of the sodium pump.
|
Selected Abbreviations and Acronyms |
|---|
|
|
Acknowledgments |
|---|
This work was supported by grants from the Deutsche Forschungsgemeinschaft/Bonn through Scho 139/20-1; the Fonds der Chemischen Industrie, Frankfurt/M; and the Giessener Hochschulgesellschaft eV, Giessen. We are grateful to Dr Klaus Failing of the Biomathematic Group of the Institute of Veterinary Physiology for his advice in handling the statistics in this study and to Dr Jack Muth for correcting the English of the manuscript.
|
Footnotes |
|---|
Reprint requests to Dr Wilhelm Schoner, Institut für Biochemie und Endokrinologie, Justus-Liebig-Universität Giessen, Frankfurter Str 100, D-35392 Giessen, Germany. E-mail schoner@vetmed.uni-giessen.de.
Received October 10, 1995; first decision October 31, 1995; accepted January 22, 1996.
|
References |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
1. DeWardener HE, Clarkson EM. Concept of natriuretic hormone. Physiol Rev. 1985;65:658-759.
2. Haddy FJ, Buckalew VM Jr. Endogenous digitalis-like factors in hypertension. In: Laragh JH, Brenner BM, eds. Hypertension: Pathophysiology, Diagnosis, and Management. 2nd ed. New York, NY: Raven Press Publishers; 1995:1055-1067.
3. Goto A, Yamada K, Yagi N, Yoshioka M, Sugimoto T. Physiology and pharmacology of endogenous digitalis-like factors. Pharmacol Rev. 1992;44:377-399. [Medline] [Order article via Infotrieve]
4. Schoner W. Endogenous digitalis-like factors. Prog Drug Res. 1993;41:249-291. [Medline] [Order article via Infotrieve]
5. Hamlyn JM. Discovery of endogenous ouabain: a new mammalian hormone. In: Bamberg E, Schoner W, eds. The Sodium Pump Structure, Mechanism, Hormonal Control and its Role in Disease. Darmstadt, FRG: Steinkopff; New York, NY: Springer-Verlag; 1994:722-731.
6. Laredo J, Hamilton BP, Hamlyn JM. Ouabain is secreted by bovine adrenocortical cells. Endocrinology. 1994;135:794-797. [Abstract]
7. Hamlyn JM, Manunta P. Ouabain, digitalis-like factors and hypertension. J Hypertens. 1992;10(suppl 7):S99-S111.
8.
Tymiak AA, Norman JA, Bolgar M, DiDonato GC, Lee H,
Parker WL, Lo L-C, Berova N, Nakanishi K, Haber E, Haupert GA.
Physicochemical characterization of a ouabain isomer isolated from
bovine hypothalamus. Proc Natl Acad Sci U S A. 1993;90:8189-8193.
9. Goto A, Ishiguro T, Yamada K, Ishii M, Yoshioka M, Eguchi C, Shimora M, Sugimoto T. Isolation of a urinary digitalis-like factor indistinguishable from digoxin. Biochem Biophys Res Commun. 1990;173:1093-1101. [Medline] [Order article via Infotrieve]
10.
Shaikh IM, Lau BWC, Siegfried BA, Valdes R Jr.
Isolation of digoxin-like immunoreactive factors from mammalian
adrenal cortex. J Biol Chem. 1991;266:13672-13678.
11. Poston L. Sodium transport inhibitors in pregnancy-induced hypertension. Cardiovasc Drugs Ther. 1990;4:351-356.
12. Lichtstein D, Gati I, Samuelov S, Berson D, Rozenman Y, Landau L, Deutsch J. Identification of digitalis-like compounds in human cataractous lenses. Eur J Biochem. 1993;216:261-268. [Medline] [Order article via Infotrieve]
13.
Bagrov AY, Fedorova OV, Austin-Lane JL, Dimitrieva RI,
Andersen DE. Endogenous marinobufagenin-like
immunoreactive factor and Na+,K+-ATPase
inhibition during voluntary hypoventilation.
Hypertension. 1995;26:781-788.
14.
Minta A, Tsien RY. Fluorescent
indicators for cytosolic sodium. J Biol
Chem. 1989;264:19449-19457.
15. Terano Y, Tomii A, Masugi F. Production and characterization of antibodies to ouabain. Jpn J Med Sci Biol. 1991;44:123-139. [Medline] [Order article via Infotrieve]
16.
Harris DW, Clark MA, Fisher JF, Hamlyn JM, Kolbasa KP,
Ludens JH, DuCharme DW. Development of an immunoassay for
endogenous digitalislike factor.
Hypertension. 1991;17:936-943.
17. Rauch AL, Buckalew VM Jr. Characterization of a competitive and reversible ligand to E2 conformation of Na,K ATPase molecule. Biochem Biophys Res Commun. 1988;150:648-654. [Medline] [Order article via Infotrieve]
18.
Hamlyn JM, Harris DW, Ludens JH.
Digitalis-like activity in human plasma: purification, affinity and
mechanism. J Biol Chem. 1989;264:7395-7407.
19. Wenzel M, Heidrich E, Kirch U, Moreth-Wolfrat K, Wizemann V, Schoner W. Increased concentrations of a circulating sodium pump inhibitor in essential hypertension and uremia and its partial purification from hemofiltrate. Physiol Bohemoslovaca. 1990;39:79-85.
20. Dixon WJ. BMDP Statistical Software Manual. Los Angeles, Calif: University of California Press; 1992.
21. Haddy F, Overbeck HW. The role of humoral agents in volume expanded hypertension. Life Sci. 1976;19:935-947. [Medline] [Order article via Infotrieve]
22.
Blaustein MP. Sodium ions, calcium ions, blood
pressure regulation, and hypertension: a reassessment and a
hypothesis. Am J Physiol. 1977;232:C165-C173.
23. Hamlyn JM, Manunta P, Hamilton BP. Endogenous ouabain in the pathogenesis of hypertensive and cardiovascular disorders. In: Laragh JH, Brenner BM, eds. Hypertension: Pathophysiology, Diagnosis, and Management. 2nd ed. New York, NY: Raven Press Publishers; 1995:1069-1081.
24.
Balzan S, Ghione S, Bives P, Gazetti P, Montali
U. Partial purification of endogenous
digitalis-like compound(s) in cord blood. Clin
Chem. 1991;37:277-281.
25.
Eliades D, Swindall B, Johnston J, Pamnani M, Haddy
F. Hemodynamic effects of bufalin in the
anesthetized dog. Hypertension. 1989;13:690-695.
26. Pamnani MB, Chen S, Yuan CM, Haddy FJ. Chronic blood pressure effects of bufalin, a sodium-potassium ATPase inhibitor, in rats. Hypertension. 1994;23(suppl I):I-106-I-109.
27. Sich B, Kirch U, Antolovic R, Schoner W. Demonstration of inhibitors of the sodium pump in human plasma and bovine adrenals crossreacting with proscillaridin A antibodies. In: Bamberg E, Schoner W, eds. The Sodium Pump Structure, Mechanism, Hormonal Control and its Role in Disease. Darmstadt, FRG: Steinkopff; New York, NY: Springer-Verlag; 1994:767-770.
28. Sweadner KJ. Multiple digitalis receptors: a molecular perspective. Trends Cardiovasc Med. 1993;3:2-6.
This article has been cited by other articles:
 |
|
 |
|
  A. Y. Bagrov, J. I. Shapiro, and O. V. Fedorova Endogenous Cardiotonic Steroids: Physiology, Pharmacology, and Novel Therapeutic Targets Pharmacol. Rev., March 1, 2009; 61(1): 9 - 38. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 W. Schoner and G. Scheiner-Bobis Role of endogenous cardiotonic steroids in sodium homeostasis Nephrol. Dial. Transplant., September 1, 2008; 23(9): 2723 - 2729. [Full Text] [PDF]
|
|
|
|
 |
|
 W. Schoner and G. Scheiner-Bobis Endogenous and exogenous cardiac glycosides: their roles in hypertension, salt metabolism, and cell growth Am J Physiol Cell Physiol, August 1, 2007; 293(2): C509 - C536. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 M. Yoshika, Y. Komiyama, M. Konishi, T. Akizawa, T. Kobayashi, M. Date, S. Kobatake, M. Masuda, H. Masaki, and H. Takahashi Novel Digitalis-Like Factor, Marinobufotoxin, Isolated From Cultured Y-1 Cells, and Its Hypertensive Effect in Rats Hypertension, January 1, 2007; 49(1): 209 - 214. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 J. A. Wasserstrom and G. L. Aistrup Digitalis: new actions for an old drug Am J Physiol Heart Circ Physiol, November 1, 2005; 289(5): H1781 - H1793. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 M. A. Pullen, D. P Brooks, and R. M. Edwards Characterization of the Neutralizing Activity of Digoxin-Specific Fab toward Ouabain-Like Steroids J. Pharmacol. Exp. Ther., July 1, 2004; 310(1): 319 - 325. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 H. Rosen, V. Glukhman, T. Feldmann, E. Fridman, and D. Lichtstein Cardiac Steroids Induce Changes in Recycling of the Plasma Membrane in Human NT2 Cells Mol. Biol. Cell, March 1, 2004; 15(3): 1044 - 1054. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 O. V. Fedorova, D. E. Anderson, E. G. Lakatta, and A. Y. Bagrov Interaction of NaCl and behavioral stress on endogenous sodium pump ligands in rats Am J Physiol Regulatory Integrative Comp Physiol, July 1, 2001; 281(1): R352 - R358. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
O. V. Fedorova, N. I. Kolodkin, N. I. Agalakova, E. G. Lakatta, and A. Y. Bagrov Marinobufagenin, an Endogenous {{alpha}}-1 Sodium Pump Ligand, in Hypertensive Dahl Salt-Sensitive Rats Hypertension, February 1, 2001; 37(2): 462 - 466. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 O. V. Fedorova, E. G. Lakatta, and A. Y. Bagrov Endogenous Na,K Pump Ligands Are Differentially Regulated During Acute NaCl Loading of Dahl Rats Circulation, December 12, 2000; 102(24): 3009 - 3014. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
R. I. Dmitrieva, A. Y. Bagrov, E. Lalli, P. Sassone-Corsi, D. M. Stocco, and P. A. Doris Mammalian Bufadienolide Is Synthesized From Cholesterol in the Adrenal Cortex by a Pathway That Is Independent of Cholesterol Side-Chain Cleavage Hypertension, September 1, 2000; 36(3): 442 - 448. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 R. Antolovic, H. Kost, M. Mohadjerani, D. Linder, M. Linder, and W. Schoner A Specific Binding Protein for Cardiac Glycosides Exists in Bovine Serum J. Biol. Chem., June 26, 1998; 273(26): 16259 - 16264. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. Y. Bagrov, O. V. Fedorova, R. I. Dmitrieva, W. N. Howald, A. P. Hunter, E. A. Kuznetsova, and V. M. Shpen Characterization of a Urinary Bufodienolide Na+,K+-ATPase Inhibitor in Patients After Acute Myocardial Infarction Hypertension, May 1, 1998; 31(5): 1097 - 1103. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
R. Schneider, V. Wray, M. Nimtz, W. D. Lehmann, U. Kirch, R. Antolovic, and W. Schoner Bovine Adrenals Contain, in Addition to Ouabain, a Second Inhibitor of the Sodium Pump J. Biol. Chem., January 9, 1998; 273(2): 784 - 792. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
O. V. Fedorova, M. I. Talan, N. I. Agalakova, E. G. Lakatta, and A. Y. Bagrov Endogenous Ligand of {alpha}1 Sodium Pump, Marinobufagenin, Is a Novel Mediator of Sodium Chloride-Dependent Hypertension Circulation, March 5, 2002; 105(9): 1122 - 1127. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||