The factors controlling the pulmonary vascular resistance (PVR) under physiological conditions are poorly understood. We have previously reported on an apparent cross-talk between the airway and adjacent pulmonary arterial bed where a factor likely derived from the bronchial epithelial cells reduced the magnitude of agonist-stimulated force in the vascular smooth muscle. The main purpose of this investigation was to evaluate whether bronchial epithelial cells release a pulmonary arterial smooth muscle relaxant factor. Conditioned media from SPOC-1, or BEAS-2B a rat- and human-derived bronchial epithelial cell lines respectively, were utilized. This media significantly relaxed pre-contracted adult but not fetal pulmonary arterial muscle in an oxygen tension-dependent manner. This response was mediated via soluble guanylate cyclase, involving AKT/PI3-kinase and neuronal nitric oxide synthase. Airway epithelial cell conditioned media increased AKT phosphorylation in pulmonary smooth muscle cells (SMC) and reduced intracellular calcium change following ATP stimulation to a significantly greater extent than observed for bronchial SMC. The present data strongly supports the evidence for bronchial epithelial cells releasing a stable and soluble factor capable of inducing pulmonary arterial SMC relaxation. We speculate that under physiological conditions the maintenance of a low pulmonary vascular resistance, postnatally, is in part modulated by the airway epithelium.