CYCLOOXYGENASE ISOENZYME LOCALIZATION AND MESSENGER-RNA EXPRESSION INRAT LUNGS

Prostanoid generation may proceed via both isoforms of cyclooxygenase, Cox-1 and Cox-2. Cox-1 is thought to be ubiquitously expressed, where as Cox-2 is mostly assumed to be dynamically regulated, responding to inflammatory stimuli. The cellular localization of Cox-1 and Cox-2 in the lung, an organ with high cyclooxygenase activity, is not known. In normal rat lungs the expression and localization of Cox-1 and Cox-2 w ere examined with immunogold-silver staining and the RT-PCR technique. Quantitative image analysis of the staining intensity was performed b y measuring mean gray values of digitized epipolarization images. Expr ession of both Cox-1 and Cox-2 was readily detectable in rat lungs. Co x-1 immunoreactivity localized predominantly to bronchial epithelial c ells, smooth muscle cells of large hilum veins, and (with lower expres sion) to alveolar macrophages and pulmonary artery endothelial cells. The most intense Cox-2 staining was noted in macrophage-and mast cell- like cells, detected in close vicinity to the bronchial epithelium and in the connective tissue surrounding the vessels. In addition, strong Cox-2 expression was found in smooth muscle cells of partially muscul ar vessels and large veins of the hilum. Bronchial epithelial cells di splayed Cox-2 immunoreactivity with limited intensity. Alveolar macrop hages and alveolar septal cells were only occasionally stained with an ti-Cox-2 antibodies. Both Cox-1 and Cox-2 are constitutively expressed in several cell types of normal rat lung, but display clearly differe nt patterns of cellular localization. Cox-2 may not be related only to lung inflammation, but is suggested to be implicated in regulatory pr ocesses under physiological conditions as well.