Pulse Pressure Correlates in Humans With a Proscillaridin A Immunoreactive Compound

Abstract

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 2×10 ⁻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 (ED ₁ , ED ₂ , ED ₃ ) that inhibited the sodium pump of human red blood cells and cross-reacted with proscillaridin A antibodies. The concentration of the proscillaridin A immunoreactivity ED ₁ in normotensive subjects had a geometric mean of 0.1 nmol/L, with a dispersion factor of 8.77. ED ₁ 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 ED ₁ [nmol/L]=0.013×mm Hg−2.17, r =.25, P <.05), systolic pressure (log ED ₁ [nmol/L]=0.010×mm Hg−2.23, r =.32, P <.01), and pulse pressure (log ED ₁ [nmol/L]=0.019×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 (ED ₁ ) correlates with mean arterial and pulse pressures.