Environmental agents altering lung biochemistry

Environmental agents may enter the lung via the tracheobronchial tree or via the bloodstream. They can interact with lung cell metabolism and set in motion a sequence of events that leads to damage, adaptation, and repair. Biochemical signs of lung damage described include lipid peroxidation, decreased biosynthesis of macromolecules, depressed enzyme activities, and the binding of metabolites of the offending agent to tissue macromolecules. As a response to acute damage, lung can activate several biochemical pathways. The selenium-glutathione peroxidase system affords protection against lipid peroxidation and increased activity of superoxide dismutase provides oxygen tolerance. Biochemical adaptation occasionally occurs very quickly: the herbicides paraquat and diquat produce an acute loss of cellular NADPH in lung. This is accompanied by a sudden increase in pentose phosphate pathway activity. Biochemical events accompanying tissue repair following lung injury are increased synthesis of nucleic acids and of protein and enhanced enzymatic activity. The repair following lung damage caused by drugs may be inhibited by oxygen.