The present invention provides a method for treating a pulmonary disease state in mammals by protecting indigenous in vivo levels of nitric oxide in mammalian cells comprising contacting the mammalian cells with a therapeutically effective amount of a nitric oxide mediator, wherein the nitric oxide mediator is selected from the group consisting of .alpha.-keto acids having four or more carbon atoms, precursors of .alpha.-keto acids having four or more carbon atoms, and the salts thereof.