The single-bolus multiple-indicator-dilution technique was used to eva
luate pulmonary removal of tracer I-125-labeled endothelin-1 in seven
anesthetized dogs. Simultaneously, pulmonary arterial and aortic blood
samples were obtained and assayed to determine the levels of immunore
active endothelin-1. When I-125-endothelin-1 was compared with a plasm
a vascular reference (Evans blue dye), there was a single passage mean
extraction of 31 +/- 8%. In contrast, there was no significant differ
ence between immunoreactive endothelin-1 levels measured in blood samp
les from the pulmonary artery and the aorta (1.26 +/- 0.58 and 1.37 +/
- 0.50 pg/ml, respectively; P = 0.47). The absence of an arteriovenous
difference for bulk endothelin-1 across the lungs in the presence of
tracer data indicating a substantial uptake implies that an amount of
endothelin-1 quantitatively more or less equal to that removed is prod
uced by the lung. The shapes of the dilution curves suggest that the t
racer endothelin uptake by the lung is a one-way process without vascu
lar reentry of tracer. We conclude that the dog lung is an important s
ite for both uptake and release of endothelin-1.