NOS1 and serum lipopolysaccharide activity: Arginase upregulation and the resulting decreased bioavailability of NOS have been reported to contribute to the pathophysiology of disease processes in which NO signaling is dysregulated, such as aging (Berkowitz et al., 2003), hypertension (Demougeot et al., 2005), and endotoxemia (Khadour et al., 2002).