Factors regulating lamellar body volume density of type II pneumocytes in excised dog lungs

Pulmonary arterial occlusion (PAO) produces multiple alterations in the physiological/biochemical environment of lung cells as well as dysfunction of the lung's surfactant system, which is considered to play a significant role in mediating lung injury. The present studies were performed using 66 excised dog lungs to evaluate the impact of alterations in ventilation, substrate availability, alveolar CO2 tension, hydrogen ion and bicarbonate concentrations, and temperature and neural denervation on the lamellar body (LB) volume density of type II pneumocytes. Ventilating excised nonperfused dog lungs with room air (0% CO2) for 4 h at 38 degrees C resulted in severe reductions (68-77%) in LB volume density. Supplementing inspired gas with 5% CO2 prevented LB depletion, while ventilation with 2.5% CO2 moderated the severity of depletion to 17-27% of control. Ventilation with 10% CO2 tended to increase LB volume density by increasing the number of LBs per cell, whereas reductions in LB volume density predominantly resulted from a decrease in LB size. The level of ventilation had no significant effect on LB volume density independent of inspired CO2 concentration. Reducing temperature to 5 degrees C prevented LB depletion. Lung perfusion with autologous whole blood failed to moderate the severity of LB depletion during room air ventilation despite the increased availability of metabolic substrates for cellular metabolism. Adding hydrochloric acid to maintain physiologically normal hydrogen ion concentrations in the perfusing blood had a small effect in ameliorating the severity of LB depletion. These results indicate that alveolar CO2 tension and bicarbonate concentration are major factors regulating the LB content of type II pneumocytes and suggest an important link between the gas exchange and phospholipid metabolic functions of the lung.