Jones, David R., Randy M. Becker, Steve C. Hoffmann, John J. Lemasters, and Thomas M. Egan. When does the lung die? Kfc, cell viability, and adenine nucleotide changes in the circulation-arrested rat lung. J. Appl. Physiol.83(1): 247–252, 1997.—Lungs harvested from cadaveric circulation-arrested donors may increase the donor pool for lung transplantation. To determine the degree and time course of ischemia-reperfusion injury, we evaluated the effect of O2ventilation on capillary permeability [capillary filtration coefficient (Kfc)], cell viability, and total adenine nucleotide (TAN) levels in in situ circulation-arrested rat lungs.Kfcincreased with increasing postmortem ischemic time (r= 0.88). Lungs ventilated with O21 h postmortem had similarKfcand wet-to-dry ratios as controls. Nonventilated lungs had threefold (P< 0.05) and sevenfold (P< 0.0001) increases inKfcat 30 and 60 min postmortem compared with controls. Cell viability decreased in all groups except for 30-min postmortem O2-ventilated lungs. TAN levels decreased with increasing ischemic time, particularly in nonventilated lungs. Loss of adenine nucleotides correlated with increasingKfcvalues (r= 0.76). This study indicates that lungs retrieved 1 h postmortem may have normalKfcwith preharvest O2ventilation. The relationship betweenKfcand TAN suggests that vascular permeability may be related to lung TAN levels.