The lung plays an essential role in facilitating the transfer of gases between inspired air and circulation, maintaining concentrations of oxygen and carbon dioxide within plasma and tissues within the narrow range that is compatible with life. In addition to its role in gas exchange, the lung has a number of important metabolic functions. For example, surfactant is manufactured in the lung for local use in increasing pulmonary compliance and preventing atelectasis. The lung also produces and metabolizes derivatives of arachidonic acid, prostaglandins, and leukotrienes [1]. The pulmonary vasculature metabolizes substances produced locally and distally, most importantly the conversion of angiotensin I to angiotensin II by angiotensin-converting enzyme in the pulmonary endothelium [1]. Hormones that are produced via metabolism in the lung, such as angiotensin II, function as chemical messengers and exert their effects on other tissues, effecting the role of the lung as an endocrine organ [1, 2]. The pulmonary endocrine system is comprised of a diverse population of cells located throughout the epithelium of the tracheobronchial tree and alveolar spaces [1].