Effects of an endogenous ouabainlike compound on heart and aorta.

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Abstract
An endogenous ouabainlike compound (OLC) has been purified from human plasma, and mass spectrometry has shown it to be indistinguishable from plant-derived ouabain. This human OLC was tested for its effects on evoked tension in guinea pig left atria and aortic rings. The tissues were incubated at 37 degrees C in bicarbonate-buffered physiological salt solution gassed with 95% O2-5% CO2. In atria stimulated electrically at 1 Hz, 85 and 170 nM human OLC increased peak active force to 177 +/- 15% and 313 +/- 32% of control, respectively (n = 3), with little effect on the duration of contraction. On washout of the OLC, peak systolic force returned to the control level with a half-time of 4.3 +/- 0.5 minutes. Similar results were obtained with 160 nM plant-derived ouabain: peak systolic force increased to 310 +/- 31% of control (n = 4) and returned to the control level with a half-time of 3.8 +/- 0.2 minutes during washout. In aortic rings, neither 170 nM human OLC nor 160 nM plant ouabain (30-minute treatments) affected resting (unstimulated) tension, but they increased the contractions evoked by histamine (0.2-1.0 microM) to 156 +/- 13% (n = 4) and 143 +/- 6% (n = 4) of control responses, respectively. The mean half-time for washout of the OLC and plant ouabain-induced augmentation of histamine-evoked tension exceeded 35 minutes. These data show that human OLC has cardiotonic and vasotonic actions qualitatively and quantitatively similar to those observed with plant ouabain.(ABSTRACT TRUNCATED AT 250 WORDS)