PULMONARY REMOVAL AND PRODUCTION OF ENDOTHELIN IN THE ANESTHETIZED DOG

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.