Hydroxyproline contents and prolyl hydroxylase activities in lungs of rats exposed to low levels of ozone.

Exposure of adult rats to 0.8 ppm ozone enhanced collagen synthesis in the lungs. Collagen synthesis was studied by estimating hydroxyproline (Hyp) content and by following the activity of prolyl hydroxylase (PH), a crucial enzyme in the pathway of collagen biosynthesis. In the early phases (1–2 day) of ozone-induced injury, PH activity was increased twofold over control values and the amount of collagen synthesized (as estimated by Hyp formation) was double the amount of non-collagenous protein synthesized. This resulted, by the third day, in a significant increase (29%) in total lung collagen. In the later stages of the injury (3–7 day), however, increases in PH activity were more gradual, approaching 2.7 times control levels at the end of the 7-day exposure period. The synthesis of non-collagenous protein during this period increased steadily and by the 7th day the ratio of the amounts of collagen to non-collagenous protein synthesized was comparable to that of controls. When the exposed (0.8 ppm O₃/7 days) animals were placed in filtered ambient air, PH activity returned to normal in 13 days whereas Hyp content remained elevated for up to 28 days. These results suggest that environmental ozone exposure could be a contributing factor in pulmonary disorders involving lung collagen synthesis.