The Functions of Histamine
On a general level, histamine is a chemical neurotransmitter produced by the body during an allergic reaction, most noticeably causing skin, nose, throat and lung irritation (itchiness, redness, swelling, rash, cough and flem, mucosa) in response to various allergens: insect bites or topical irritants, dust pollen, food allergies. These reactions are part of the inflammatory response, which is an important part of the overall immune response. Other functions: histamine helps regulate physiological function in the gut, helps to regulate sleep, and aids the sexual response.
Let’s look at these functions one by one, beginning with how histamine functions as a chemical neurotransmitter.
Histamine as a Neurotransmitter: A neurotransmitter is a chemical that is passed between neurons in the nervous system. When a neuron releases molecules of a chemical neurotransmitter, it passes from what is called the “presynaptic nerve terminal” or the end of the neuron, through the “synapse” or the gap between neurons, and is finally taken up by a “receptor” area on the receiving neuron. That neuron then continues to pass the neurotransmitter, resulting in a reaction. The constant stimulation of neurons causes reactions in the body which are specific to the type of neurotransmitter that is passed.
Histamine is grouped with a class of neurotransmitters called “Small Molecule Neurotransmitter Substances,” alongside Serotonin, Epinephrine (adrenaline) and Dopamine.
Histamine in Allergic Reactions: There is always a small amount of histamine circulating through your body at any given time. When a foreign substance is introduced, such as the toxic chemicals of an insect bite or the oil of poison plants like poison ivy, the body releases larger amounts of histamine to the site of infection. In individuals who are allergic to certain types of food like strawberries or foods containing sulfur, the body can release very large quantities of histamine which can result in shock and sometimes death. The body cannot handle large amounts of histamine. As a result, the body will counter-act histamine by producing Epinephrine (adrenaline) which helps to de-activate histamine. Sometimes high levels of adrenaline can result in unwanted anxiety and panic attacks. Medication like Benadryl or other antihistamines help to clear some histamine from the body for relief. This is why, whenever you are sick with a head cold, you want to take medicine that contains antihistamine, to relieve swelling resulting from infection inside the nasal cavity and stimulate fluid secretion.
What is the purpose of histamine in allergic reactions? : The histamine reaction in relation to the immune response (in both allergic reactions and immune reactions) serves two main functions: 1. It causes what is called “vasodilation.” Vasodilation occurs when the muscular walls that surround blood vessels are relaxed, causing the interior of the blood vessel to widen. 2. It induces fluid secretion at the site of infection. Both of these responses are an important part of the inflammatory response. Vasolidation allows white blood cells to move easily to the site of infection. Fluid secretion is important in ridding the body of infectious agents or allergens. It is also known, at a molecular level, that histamine helps to stimulate certain macrophage responses as well as Helper T cell responses, and so it is purported through the latter that histamine also helps induce antibody response.
Histamine in Digestion: Histamine plays a role in gastric secretion by helping to induce the production of acid in the stomach.
Histamine in Sleep: The body regulates the amount of histamine in circulation and maintains a careful balance. This is most important with keeping the body awake and alert. Antihistamines are known to cause drowsiness and sleep.