Early physiologic and biochemical effects of thoracic X-irradiation on the pulmonary surfactant system.

A study of surfactant physiology and biochemistry was undertaken in mice who received varying doses of X-irradiation to the thorax. During the first 12 weeks after X-irradiation, the period which precedes radiation pneumonitis, there is an increase in the amount of DPC in both the lung and the alveolar surface lining layer. This increase begins about 7 days after irradiation, returns to control levels by 12 weeks, and coincides with a fall in the total number of AM's. Over-all synthesis of DPC in the lung and its transport to the alveolar surface, as determined by incorporation of 3H from glycerol and 14C from palmitate into PC in vivo, remained unchanged from control levels. These results may be explained in part by proliferation of type 2 pneumocytes following X-irradiation and by decreased removal of surfactant from the alveolar surface, possibly as a result of the depletion of the AM population. No changes in mechanical properties of the lung or in situ E tis or E surf occurred at this stage, nor were changes detected in the surface properties of the alveolar lavage fluid.