Endothelin-1-like immunoreactivity in human urine

By using a radioimmunoassay specific for endothelin-1 (ET-1), we studied whether ET-1-like immunoreactivity (LI) is present in human urine. Significant amounts of ET-1-LI were present in human urine, and the daily urinary excretion of ET-1-LI in 30 normal subjects was 67.6 +/- 35.5 ng/day. The mean urinary excretion of ET-1-LI determined in spot urine was 82.8 +/- 38.2 pg/mg creatinine (n = 30), while the mean plasma concentrations of ET-1-LI in the same individuals were 1.1 +/- 0.5 pg/ml. There was no significant correlation between urinary ET-1-LI excretion and its plasma levels. Reverse-phase high-pressure liquid chromatography of human urine extract revealed a major ET-1-LI component coeluting with standard ET-1. The present study demonstrates the presence of ET-1-LI excreted in human urine, although its exact source and physiological significance in renal tissues remain to be determined.