Adrenaline, or epinephrine, is a stress hormone secreted from the adrenal glands on the kidneys. It plays a major role in preparing the body for a fight-or-flight reaction in threatening environments. An adrenaline rush is a sudden increase in the secretion of adrenaline from the adrenal glands. This happens when the brain communicates to the glands that there will be a need for a fight-or-flight response. The cause of an adrenaline rush need not be an actual physical threat but can also be an imagined threat, strenuous exercise, heart failure, chronic stress, anxiety or a disorder of the brain or adrenal glands.
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When you perceive something as threatening or exciting, the hypothalamus in the brain signals to the adrenal glands that it's time to produce adrenaline and other stress hormones. The adrenal glands produce adrenaline by transforming the amino acid tyrosine into dopamine. Oxygenation of dopamine yields noradrenaline, which is then converted into adrenaline. Adrenaline binds to receptors on the heart, arteries, pancreas, liver, muscles and fatty tissue. By binding to receptors on the heart and arteries, adrenaline increases heart rate and respiration, and by binding to receptors on the pancreas, liver, muscles and fatty tissue, it inhibits the production of insulin and stimulates the synthesis of sugar and fat, which the body can use as a fuel in fight-or-flight situations.
An adrenaline rush can have detrimental effects on health. In people with heart disease, it can cause a weakening of the heart muscle, heart failure or a heart attack. It can also affect the brain in negative ways. Continuous heightened levels of stress hormones can lead to a shrinkage of the hippocampus, the brain's main memory center, according to a research team in the January 2008 issue of PNAS. Stress hormone stimulates the production of IL-1 beta, a cytokine, or signaling molecule, that creates inflammation in the hippocampus and prevents the formation of new neurons. IL-1 beta also binds to sites in the hypothalamus, pituitary and the hippocampus, the researchers found.
While hyperactivity in the adrenal gland can have detrimental effects on health, mildly increased levels of stress hormones can have positive effects on the blood content of leptin, a protein that is produced in the body's white fatty tissue and that accelerates the growth of cancer cells, according to a research team in the July 2010 issue of Cell. While the blood content of leptin normally is directly proportional to the amount of fatty tissue in the body, stress hormones may play a role in regulating how much leptin the fatty cells produce. The less they produce, the slower cancer cells will grow, the researchers say.
Stress Hormones and Memory
While adrenal glands constitute a major site for adrenaline synthesis, adrenergic neurons in the brain stem also produce adrenaline. These neurons contain the enzyme PNMT, which is required for a gland or neuron to convert noradrenaline into adrenaline. Stressful situations accelerate the activity of adrenergic and noradrenergic neurons. This can have a profound, negative effect on memory, according to a research team in the October 2008 Journal of Neuroscience. When stress chemicals function as neurotransmitters, they affect the storage of memories by activating the amygdala, a center of the brain involved in the processing and storage of negative emotions. Normally, people remember things better if they are replayed many times in the mind, but a single emotionally significant event may suffice for neurons to generate long-lasting networks.
Intermittent adrenaline rushes occurring for natural reasons do not require treatment. If chronic stress, anxiety or panic disorder triggers an excessive secretion of adrenaline, anti-anxiety medications, such as selective serotonin reuptake inhibitors, can alleviate symptoms by blocking the trigger. Beta-blockers, which bind to receptors on the heart, are commonly used to prevent a failing heart from going into overdrive from an excessive secretion of stress hormones. According to a report published in the February 2007 issue of Nature Medicine, another treatment for heart patients still under investigation consists in blocking adrenal gland GRK2, an enzyme that regulates adrenaline secretion.