A SENSITIVE RADIOIMMUNOASSAY MEASURING ENDOTHELIN-LIKE IMMUNOREACTIVITY IN HUMAN PLASMA - COMPARISON OF LEVELS IN PATIENTS WITH ESSENTIAL-HYPERTENSION AND NORMOTENSIVE CONTROL SUBJECTS

1. A radioimmunoassay has been developed for measuring edothelin-like immunoreactivity in human plasma using an antibody raised against endothelin-1 which also cross-reacts with big edothelin-1 and endothelin-2 but not endothelin-3. 2. The sensitivity of the assay was 1 fmol/tube with inter- and intra-assay coefficients of variation of 13% and 9% respectively. Cross-reactivity with endothelin-3 and non-endothelin peptides was less than 1%. 3. Endothelin-like immunoreactivity was present in the plasma of hypertensive patients (n = 259) at a concentration of 5.7 ± 0.5 pmol/l (mean ± SEM), which was not significantly different from that of age-matched control subjects (5.1 ± 0.5 pmol/l). At these levels, endothelin-1 is unlikely to function as a circulating hormone. 4. Within the normotensive group, the concentration of endothelin-like immunoreactivity in plasma was positively correlated with mean arterial blood pressure, but in hypertensive patients it showed a significant negative correlation.