Is big endothelin converted to endothelin-1 in circulating blood?

Although evidence has been accumulating to support an intracellular processing of big endothelin-1 (big ET-1) to ET-1, molecular conversion in the circulating blood remains to be elucidated. The present study was undertaken to investigate whether big ET-1 was converted to ET-1 in human blood. In the first experiment, normal serum with synthetic big ET-1 exogenously added or serum from patients with chronic renal failure was incubated in vitro at 37 o C for 1 h. In the second experiment, synthetic big ET-1 was incubated in the whole blood at 37 o C for 1 h