Tyrosine kinase activation during lung injury, fibrosis, and compensatory lung growth

Endobronchial instillation of paraquat into left lungs of rats resulted in ipsilateral fibrosis (evaluated by light and electron microscopy) and compensatory growth of the contralateral lung. Tyrosine kinase (Tyr-K) activity rose early in the fibrotic lung, peaked to a value 4 times the controls on day 3, and remained elevated on day 14. In the right lung, slight increase in activity occurred only on day 5. Cellular proliferative activity was inhibited in both lungs early after injury. In the right lung, however, DNA synthesis increased to levels 10 times the controls by day 7. In the left lung, the inhibition decreased gradually after day 7, indicating increased cellular proliferation. We conclude that activation of some cellular Tyr-K may play a role in regulating early cellular proliferation during lung injury, fibrosis, and compensatory growth.