Research

Upregulation of nitric oxide synthase in mice with severe hypoxia-induced pulmonary hypertension

Karen A Fagan^1,2 , Brian Morrissey¹, Brian W Fouty^1,2, Koichi Sato², Julie Wright Harral¹, Kenneth G Morris Jr², Marloes Hoedt-Miller¹, Shanda Vidmar², Ivan F McMurtry^1,2 and David M Rodman^1,2

¹  Division of Pulmonary Sciences and Critical Care Medicine, University of Colorado Health Sciences Center, Denver, Colorado, USA

²  Cardiovascular Pulmonary Research Laboratory, University of Colorado Health Sciences Center, Denver, Colorado, USA

author email corresponding author email

Respiratory Research 2001, 2:306-313doi:10.1186/rr74

Published:	4 September 2001

Abstract

Background

The importance of nitric oxide (NO) in hypoxic pulmonary hypertension has been demonstrated using nitric oxide synthase (NOS) knockout mice. In that model NO from endothelial NOS (eNOS) plays a central role in modulating pulmonary vascular tone and attenuating hypoxic pulmonary hypertension. However, the normal regulation of NOS expression in mice following hypoxia is uncertain. Because genetically engineered mice are often utilized in studies of NO, we conducted the present study to determine how hypoxia alters NOS expression in wild-type mice.

Method

Mice were exposed to sea level, ambient conditions (5280 feet) or severe altitude (17,000 feet) for 6 weeks from birth, and hemodynamics and lung NOS expression were assessed.

Results

Hypoxic mice developed severe pulmonary hypertension (right ventricular systolic pressure [RVsP] 60 mmHg) as compared with normoxic mice (27 mmHg). Using quantitative reverse-transcription PCR, it was found that expressions of eNOS and inducible NOS (iNOS) increased 1.5-fold and 3.5-fold, respectively, in the lung. In addition, the level of lung eNOS protein was increased, neuronal NOS (nNOS) protein was unchanged, and iNOS was below the limit of detection. Immunohistochemistry demonstrated no change in lung iNOS or nNOS staining in either central or peripheral areas, but suggested increased eNOS in the periphery following hypoxia.

Conclusion

In mice, hypoxia is associated with increases in lung eNOS, possibly in iNOS, but not in nNOS; this suggests that the pattern of lung NOS expression following hypoxia must be considered in studies using genetically engineered mice.