Lung lysyl oxidase activity: relation to lung growth

The activity of lysyl oxidase (LOX), the extracellular enzyme responsible for initiating crosslinking of collagen and elastin, was measured during 3 types of postnatal lung growth. Lung parenchymal and pleural LOX activity was high in the first 3 wk of of life, decreasing by 50 % to stable amounts by 4 to 10 wk. In contrast, airway and aortic LOX activity remained high during the first 10 wk of life, decreasing by 50 to 75 % thereafter. After pneumonectomy, lung LOX activity doubled within 24 h, decreasing to control values thereafter. Hypoxia (12 to 13 % O2) resulted in a prompt and sustained increase in lung but not pleural, airway, or aortic LOX activity. Thus, LOX activity can be controlled precisely within specific tissues and appears to be related to early phases of connective-tissue synthesis. Further studies of the synthesis and degradation of LOX should provide important information about the control of connective-tissue formation within the lungs.