Effects of cigarette smoke on nitric oxide synthase expression in the rat lung

To examine the effects of cigarette smoke on nitric oxide synthase (NOS) ge ne expression and protein production, groups of rats were exposed to smoke once only or daily and were sacrificed after 1, 2, 7, or 28 days of exposur e. NOS-I, NOS-2, and NOS-3 mRNAs in whole lung were quantified using revers e transcription polymerase chain reaction (RT-PCR), and NOS protein levels were determined by Western blots. Neither NOS-1 gene expression nor protein levels changed with smoke exposure. Levels of NOS-2 expression were more t han doubled in smokers at Day 1 and decreased to control values during 1 mo nth with daily smoke exposure, while protein levels did not change. NOS-3 e xpression was increased approximately 35% after 2 days of smoke exposure an d remained increased to 28 days, whereas protein levels were increased by a pproximately 60% ai Day 7 and remained elevated. In situ hybridization show ed that NOS-2 was diffusely expressed in the lung parenchyma, airways, and vessels, and that NOS-3 was strongly expressed in vascular endothelium. Pro tein distribution, as determined by immunohistochemical staining, was ident ical to mRNA tissue distribution, and these distributions were not changed by smoke. We conclude that smoke exposure induces a rapid but transient inc rease in transcription of NOS-2, and a sustained increase in transcription and translation of NOS-3; up-regulation of NOS occurs within the anatomic c ompartment where these genes are normally expressed. These findings indicat e that cigarette smoke can directly and rapidly affect NOS expression, and thus potentially affect the function of the pulmonary vasculature.