Pulse Pressure Correlates in Humans With a Proscillaridin A Immunoreactive Compound

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 2 x 10(-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] = 0.013 x mm Hg-2.17, r = .25, P < .05), systolic pressure (log ED1 [nmol/L] = 0.010 x mm Hg-2.23, r = .32, P < .01), and pulse pressure (log ED1 [nmol/L] = 0.019 x mm 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.

Bovine Adrenals Contain, in Addition to Ouabain, a Second Inhibitor of the Sodium Pump

“…Derivatives of cardiotonic steroids with a UV maximum at 250 nm have been described (30), but the molecular mass and the mass fragmentation pattern of inhibitor A is inconsistent with hitherto known cardiotonic steroids; it is also unlikely that the more hydrophilic inhibitor A is a degradation product of ouabain (inhibitor B). Inhibitor A resembles in its retention time and immunological properties the substance whose concentration was found elevated in humans with increased systolic blood pressure (but not diastolic blood pressure) and hence increased pulse pressure (20). Apparently, the type of action of inhibitor A differs from that of ouabain.…”

“…Inhibition of 86 RbCl Uptake into Red Blood Cells-This was essentially performed as described previously using a silicon oil centrifugation technique in Eppendorf cups (20,22).…”

“…Starting from the idea that mammals may, like toads, be able to synthesize bufadienolides, we recently demonstrated that a compound is circulating in increased concentrations in patients with hypertension, which cross-reacts with antibodies against proscillaridin A (20). The compound differed in its mode of action from ouabain insofar as its concentration did not correlate with the diastolic blood pressure, albeit it had a similar HPLC 1 retention time to that of ouabain.…”

Endogenous Na,K Pump Ligands Are Differentially Regulated During Acute NaCl Loading of Dahl Rats

“…Recent studies have shown that mammalian tissues also contain bufadienolide CS. [5][6][7] Bufadienolides were discovered in amphibians and differ from cardenolides in having a 6-membered doubly unsaturated lactone ring. 5 One CS that was purified from human urine by high-performance liquid chromatography mass spectrometrically was identical to an amphibian bufadienolide, marinobufagenin (MBG).…”

A Specific Binding Protein for Cardiac Glycosides Exists in Bovine Serum

“…Among those are the cardenolides ouabain or its isomer (6 -9), digoxin (10), and the bufadienolides 19-norbufalin (11) and marinobufagenin (12,13). Additional, yet unknown, substances seem to exist (14). Ouabain or its isomer has been shown to be secreted from bovine cortical adrenal cells of the zona glomerulosa in tissue culture (15,16) stimulated with angiotensin II (17).…”