The effect of NO2 exposure on perfusate distribution in isolated rat lungs: pulmonary versus bronchial circulation.

Isolated rat lung (IPL) studies have suggested that the pulmonary uptake of inhaled nitrogen dioxide (NO2) is governed via a chemical reaction-dependent process which results in NO2-derived reaction products diffusing into the vascular space. Experimental results indicated that substantial proportions of this reactive absorption occur in distal sites. However, gas phase deposition in proximal locations cannot be ruled out due to the lack of information on bronchial perfusion in rat IPL preparations. Consequently, we evaluated the presence of pulmonary-to-bronchial anastomotic perfusate flow in control and NO2-exposed (10.3 ppm) rat IPL. Monastral blue (MB) was used as a vascular marker and was infused into the pulmonary artery catheter either for recirculation at time zero or as an end-experiment (60 min) bolus. In addition, MB was infused into control in situ preparations to observe intact bronchial circulations. Lungs were prepared for routine evaluation by light microscopy. In situ MB was observed in all pulmonary and bronchial vessels. In IPL, MB was observed only in far terminal airway-associated vessels. No differences were observed in MB distribution between bolus (end-experiment) and recirculated (time zero) applications. NO2 exposure produced no effect on MB distribution. We conclude that in rat IPL: (1) negligible anastomotic flow occurs from the pulmonary into the bronchial circulation, (2) nonedemagenic NO2 exposures do not alter existing perfusate distribution, and (3) the perfusate appearance of inhalation-derived species results from gas phase deposition only in distal sites which have ready accessibility to the pulmonary circulation.