The human body has many mechanisms that signal that something is not right. For instance, a fever indicates the presence of a harmful pathogen, thirst is a natural response to dehydration, and feeling pain brings about an awareness that damage is occurring within the body. In turn, the body may release hormones or other molecules that help overcome the crisis.
We have known for some time that endorphins act as a natural analgesic, that is, it is a natural pain reliever. They are considered endogenous opioids because they bind to the same cell surface receptor as do opium and morphine, and hence have similar effects. There are many myths surrounding the release of endorphins into the blood stream. Many people believe that endorphins are released when one is happy, during orgasms, even when someone smiles. The truth is, that there is NO scientific evidence supporting these claims. In fact, the level of endorphins in the blood stream has been shown to decrease during sex8.
Endorphins are released in the body in response to pain, or extraneous exercise. Simply put, they prevent someone from feeling the pain associated with tissue damage. β-endorphin is a 31-amino-acid-peptide that functions as a neurotransmitter, that is, its target cell is a neuron. β-endorphin is released from the anterior pituitary gland in response to a pain signal that has been sent to the hypothalamus. It then enters the blood stream.
Let’s first look at the pain signal. There are pain receptors throughout the body, called nociceptors. When tissues are damaged, they release a variety of substances, such as histamine, potassium and arachidonic acid. These substances stimulate the nerves and cause the release of Substance-P, which activates the pain pathway and transmits the pain signal to the central nervous system. In this way, the brain not only recognizes pain, but it also commits its source to memory. It is this recognition that creates the reflex to move away from the source of the pain.
The opiate receptor is located on the neurons that release Substance-P. When β-endorphin is release in response to pain, it will bind to this receptor and as a result Substance-P will not be released. Therefore, the pain pathway will not be initiated, or will be reduced. β-endorphin is quickly degraded by an enzyme, and the receptor will then be free to bind to its substrate again. If this degradation process did not take place, then the feeling of pain will be nullified and the hand that inadvertently sat on the hot stove will remain there.
Addiction to opioids such as morphine and opium is the result of the drugs remaining on the receptors for long periods of time. A person becomes numb after a while because the receptors become “down regulated,” that is, there are less of them on the surface of the cell. Quite simply, there are fewer receptors and it takes more of the drug to find them. It then takes more of the drug to reach the same level of the “pain free” high.
The physiological role of endorphins in the human body has not yet been fully elucidated. However, one thing is clear. Its role is not to induce happiness, but to remove the pain.