Soluble guanylate cyclase gene expression and localization in rat lung after exposure to hypoxia

The nitric oxide (NO)-cGMP signal transduction pathway plays an important r ole in the regulation of pulmonary vascular tone and resistance in pulmonar y hypertension. A number of studies have demonstrated that endothelial (e) and inducible nitric oxide synthases (NOS) are upregulated in hypoxia-expos ed rat lung. These changes in NOS expression have been found to correlate w ith the process of pulmonary vascular remodeling in hypoxia-induced pulmona ry hypertension, and remodeling is increased in the absence of eNOS. In thi s study, we examined the expression and localization of soluble guanylate c yclase (sGC), the primary receptor for NO, in hypoxia- and normoxia-treated rat lungs. Male Sprague-Dawley rats were exposed to hypoxia (10% O-2, norm obaric) or normoxia for 1, 3, 5, and 21 days. The lungs were used for Weste rn analysis of sGC protein, sGC enzyme activity, immunohistochemistry using antiserum against sGC alpha(1)- and beta(1)-subunits, and nonradioactive i n situ hybridization (NRISH) using a digoxigenin-labeled sGC alpha(1)-subun it cRNA probe. Western blot analysis revealed a more than twofold increase of sGC protein alpha(1)-subunit in rat lungs exposed to 3, 5, and 21 days o f hypoxia, correlating well with sGC enzyme activity. Immunohistochemistry and NRISH demonstrated increased expression of sGC in the smooth muscle cel ls of the pulmonary arteries and arterioles in the hypoxic rat lungs when c ompared with normoxic controls. Based on our results, the upregulation of s GC may play an important role in the regulation of smooth muscle tone and p ressure in the pulmonary circulation during chronic hypoxia.