EFFECT OF ENDOTHELIN-1 ON CANINE AIRWAY BLOOD-FLOW

The effect of endothelin-I (ET-1) on the blood flow contributions of t he pulmonary and systemic circulations to the trachea and main bronchi were measured in anesthetized dogs by injecting 15-mum radiolabeled m icrospheres into the right and left heart, respectively. After the mic rosphere injections the animals were killed, and the tracheal cartilag e, tracheal muscle mucosa, and main bronchi were excised and collected for radioactive counting. The results of this study showed that under normal conditions tracheal blood flow was primarily systemic (>95% of total tracheal blood flow) averaging 25-50 ml/min/100 g, whereas both the pulmonary (9-10 ml/min/100 g) and systemic circulations (19-20 ml /min/100 g) contributed substantially to main bronchi blood flow. Admi nistration of ET-1 i. v. decreased systemic tracheal cartilage blood f low from 25.3 +/- 3.8 to 14.5 +/- 2.8 ml/min/100 g, systemic tracheal mucosal blood flow from 50.0 +/- 7.0 to 25.0 +/- 7.0 ml/min/100 g, and systemic main bronchi blood flow from 19.4 +/- 4.6 to 11.6 +/- 3.4 ml /min/100 g (p<0.05). These results indicate that ET-1 is a potent cons trictor of the airway circulation and may contribute to airway ischemi a seen in different airway disease states.