[Hypoxia impacts expression of nitric oxide synthase mRNA of different segments of intrapulmonary arteries]

To investigate expression and localization of nitric oxide synthase (cNOS) mRNA of normoxic pulmonary arteries and the impact of hypoxia on its expression.

In situ hybridization was performed on each lung sections from rats in 1-week hypoxic group, 2-week hypoxic group, and control group to detect cNOS mRNA expression and localization by using cRNA probe for NOS.

The positive score of cNOS mRNA expression by endothelial cells of pulmonary arteries associated with bronchioli was significantly higher than that of arteries associated with respiratory or terminal bronchioli (q = 8.13, 5.49, P < 0.01) in the control rats. In the 1-week hypoxic group or the 2-week hypoxic group, however, cNOS mRNA expression by endothelial cells of pulmonary arteries associated with either respiratory or terminal bronchioli was markedly decreased compared with that of the control group. No significant difference was found in cNOS mRNA expression by smooth muscle cells of each segments of pulmonary arteries (F = 2.26, P > 0.05). However, cNOS mRNA expression by smooth muscle cells of pulmonary arteries associated with respiratory bronchioli or terminal bronchioli was significantly decreased in the 1-week or the 2-week hypoxic group compared with the control group.

These findings suggest that NOS mRNA expression by endothelial cells is greater in the larger, more proximal pulmonary arteries than at the periphery. Chronic hypoxia mainly impairs cNOS mRNA expression by proximal pulmonary artery endothelial cells and periphery pulmonary artery smooth muscle cells.