Effect of short-term exposure to ozone on the lecithin metabolism of rat lung.

The effect of short-term inhalation of ozone (O3) on the content and metabolism of phospholipids, particularly lecithin (PC), in rat lung was studied. The PC level increased slightly, but significantly, in the lung of rats exposed to 2 ppm O3 for 3 h. However, the PC level remained within the control level following the exposure to 2.5 and 5 ppm of O3 for 3 h, while the lysolecithin (LysoPC) content greatly increased. The incorporation of [32P]orthophosphate (32Pi) and [14C]palmitic acid into PC in the lung slices obtained from the animals tended to increase following the exposure to 2 ppm for 3 h, but decreased following the exposure to O3 above 2.5 ppm for 3 h. On the other hand, the radioactivity of 32Pi in LysoPC of lung from the rats exposed to O3 above 2.5 ppm was significantly greater than that from the control. Such changes in the content of PC or LysoPC and in the incorporation of labeled precursors into them may be explained, at least in part, by the combination of the presently and previously observed changes in the activities of enzymes participating in PC metabolism pathway as follows: (1) the significant stimulation in the activity of LysoPC acyltransferase (LysoPC ATF), which can transfer fatty acids onto LysoPC, for palmitic acid at an earlier stage of the exposure to O3 at 2 and 2.5 ppm; (2) the depression in the activities of this enzyme and another ATF-LysoPC-LysoPC ATF, which can synthesize one molecule of disaturated PC from two moles of saturated-LysoPC-by increasing the O3 exposure time; and (3) the stimulation in the phospholipase A2 activity in the lung of rats exposed to 2 ppm of O3 for 6 h.