Presence of immunoreactive endothelin in human plasma

Abstract
A highly specific and sensitive radioimmunoassay has been established for measurement of human endothelin (hET) in human plasma. After extraction of plasma with an octyl‐silica column, this assay allowed for detection of immunoreactive (IR) hET as low as 0.2 fmol/ml. In 16 healthy subjects, the mean concentration of plasma IR‐hET was 0.6 fmol/ml. Reverse‐phase HPLC coupled with radioimmunoassay revealed two major IR‐hET components, one corresponding to authentic hET(1–21) and another with more hydrophilicity than hET(1–21). These data indicate that ET is a circulating vasoconstrictor hormone in man.