Elevated norepinephrine may be an etiological factor in a wide range of diseases: Age-related macular degeneration, systemic lupus erythematosus, atrial fibrillation, metabolic syndrome

The neurotransmitter norepinephrine (NE) participates in a broad range of physiological functions, both in the brain and in the periphery, where it is a principal output molecule of the sympathetic nervous system. NE receptors are present in nearly all, if not all, organs of the body, which may allow this molecule to play a role in a variety of disease processes. This paper examines the hypothesis elevated NE signaling, through genetics and/or environmental factors, is an etiological factor in a variety of diseases outside of the brain, including age-related macular degeneration, systemic lupus erythematosus, atrial fibrillation, and metabolic syndrome. Lines of evidence presented to assess the hypothesis include: (1) studies of noradrenergic drugs modulating the four diseases; (2) association of these diseases with bipolar disorder, hypertension, and obesity, where the latter three conditions may involve elevated NE signaling; and (3) association with psychological stress, since NE is released in response to stress. Many of the studies cited tend to support the hypothesis, or are at least consistent with it. If the hypothesis is correct, perhaps a large number of individuals would benefit from chronically taking drugs that systemically diminish noradrenergic signaling, thereby helping prevent or treat a wide variety of diseases.