[Validation of radioimmunoassay of tissue and plasma endothelin-1]

We have established a sensitive and specific radioimmunoassay for measurement of ET-1 in tissues and human plasma. Half maximal inhibition of binding of ET-1125 I was obtained at 6.6 pg/tube and the lowest concentration detectable was 0.785 pg/tube (p less than 0.001). Inter and intra-assay precisions were 14 and 9.6%, respectively. The antibody cross-reacted with ET-2 at 36.5%, ET-3 at 23.4% and Big ET at 9.9% but did not recognize non related vasoactive peptides. Immunoreactive ET-1 was extracted from human and rat tissues (lung, kidney) or human plasma using Sepak C18 columns. Human lung contains 2.3 ng/g ir-ET, corresponding mainly to synthetic ET-1 as revealed by reverse phase HPLC coupled to RIA. Rat lung and kidney ir-ET concentrations were 2.4 ng/g and 0.45 ng/g, respectively. Preliminary results indicated that the basal level of ir-ET in human plasma was 1.24 pg/ml. The RIA could be very useful to study the role of ET in various physiopathological states.