Norepinephrine, or noradrenaline, is a catecholamine that functions as a neurotransmitter and a stress hormone. High levels of norepinephrine can refer to high levels of the chemical either in the blood or in the central nervous system. Though both levels can be measured, it is considerably simpler and more common to measure norepinephrine in the blood than in the central nervous system. High concentrations of norepinephrine in the blood often correlates with insomnia and anxiety. Drugs that lower blood concentrations of norepinephrine include serotonin reuptake inhibitors, blood pressure medications, heart medications and lithium salts.
Serotonin Reuptake Inhibitors
Selective serotonin reuptake inhibitors belong to a class of drugs that have anti-depressant and anxiolytic, or anti-anxiety, effects. They block the absorption of brain serotonin back into the neurons. This leaves a larger amount of naturally occurring serotonin available for binding to serotonin receptors in the brain. Via the serotonin receptors, serotonin regulates the processing of negative emotions in the amygdala, the brain's main fear center. As fear is one of the main catalysts for the secretion of the stress chemicals cortisol, epinephrine and norepinephrine from the adrenal glands, down-regulating fear can lower blood concentrations of norepinephrine.
The newest class of anti-depressants, which selectively inhibits the reuptake of both serotonin and norepinephrine, may be even more successful in treating depression and anxiety and lowering blood concentrations of stress chemicals, according to a study in the October 2009 issue of "Journal of Medicinal Chemistry."
Blood Pressure Medications
The attention deficit hyperactivity disorder medication guanfacine is a potentially effective medication for lowering blood concentrations of norepinephrine. Guanfacine helps re-establish disrupted neural networks in the prefrontal cortex, reports a study in the April 2007 issue of "Cell." Guanfacine also lowers both the systolic blood pressure, or top reading, and the diastolic blood pressure, or bottom reading, by stimulating norepinephrine receptors in the prefrontal cortex. A stimulation of the norepinephrine receptors leads to a decrease in nerve signals from the vasomotor center to blood vessels and heart. This causes pressure in the blood vessels and heart rate to drop. It can also reduce stress hormone levels.
The main heart medications used to prevent the effects of norepinephrine are drugs in the beta blocker class. Beta blockers block the stimulating effects of stress hormones on heart contraction, heart beat, respiration and muscles by competing with the stress hormones for the available binding sites. Beta blockers do not directly lower the levels of norepinephrine, but according to a study published in the March 2009 issue of "Nature Neuroscience," the beta blocker propanolol can reduce the storage of fearful memories, which could ultimately lower secretions of stress hormones from the adrenal glands.
Lithium salts, the oldest medications used to treat psychosis, major depression and bipolar disorder, may also down-regulate the secretion of stress hormones. According to a study published in the May 2010 issue of "Journal of Lipid Research," lithium ions fight neuroinflammation by decreasing the pro-inflammatory chemical arachidonic acid and increasing the brain levels of the omega-3 fatty acid DHA. Neuroinflammation can damage neurons and disrupt neuron connections. This can increase blood concentrations of the stress hormones. By fighting the inflammation in the brain's neurons, lithium may help to down-regulate the secretion of stress hormones.
- "Journal of Medicinal Chemistry"; Synthesis of 1,1-[1-Naphthyloxy-2-thiophenyl]-2-methylaminomethylcyclopropanes and Their Evaluation as Inhibitors of Serotonin, Norepinephrine, and Dopamine Transporters; James White, et al.; September 2009
- "Cell"; α2A-Adrenoceptors Strengthen Working Memory Networks by Inhibiting cAMP-HCN Channel Signaling in Prefrontal Cortex; Min Wang, et al.; April 2007
- "Nature Neuroscience"; Beyond Extinction: Erasing Human Fear Responses and Preventing the Return of Fear; Merel Kindt, et al.; March 2009
- "The Journal of Lipid Research"; Lithium Modifies Brain Arachidonic and Docosahexaenoic Metabolism in Rat Lipopolysaccharide Model of Neuroinflammation; Mireille Basselin, et al.; May 2010