Enkephalins are naturally occurring substances produced within the body. These compounds are part of a broader group of chemicals known as endogenous opioids, which are similar to external opioid drugs. Enkephalins play a role in the body’s internal signaling systems, contributing to various physiological processes. They help the body maintain internal balance and respond to stimuli.
What Enkephalins Are
Enkephalins are small protein-like molecules called pentapeptides, composed of five amino acids. Two primary types of enkephalins have been identified: met-enkephalin and leu-enkephalin, distinguished by their final amino acid, methionine or leucine. Both are derived from a larger precursor protein called proenkephalin. The processing of proenkephalin yields multiple copies of met-enkephalin and one copy of leu-enkephalin.
These endogenous opioids are widely distributed throughout the body. High concentrations are found in the brain, including areas like the striatum, cerebral cortex, and hippocampus, as well as in the spinal cord. They are also produced in peripheral tissues, such as the adrenal medulla, and are present in the gastrointestinal tract, kidneys, testes, pancreas, heart muscle, skin tissue, lungs, joints, and bones.
How Enkephalins Exert Their Effects
Enkephalins function as neurotransmitters or neuromodulators, influencing communication between nerve cells. Their effects are mediated by binding to opioid receptors. The two main types of opioid receptors that enkephalins interact with are the delta (δ) and mu (μ) opioid receptors, with higher affinity for delta receptors.
When enkephalins bind to these receptors, they trigger intracellular signaling. This binding can inhibit the release of certain neurotransmitters, such as substance P and glutamate, which are involved in transmitting pain signals. By modulating these signals, enkephalins effectively reduce the perception of pain. This mechanism lowers the intensity of pain messages before they reach higher brain centers.
Major Physiological Functions
Enkephalins are involved in the body’s pain modulation system, acting as natural painkillers. When released, they decrease the sensation of pain, a process known as nociception, and promote analgesia. This pain-relieving action occurs by binding to opioid receptors in the spinal cord and various brain regions, thereby activating pathways that suppress pain signals.
Beyond pain relief, enkephalins also play a role in mood regulation and the body’s response to stress. Their mood-modulating effects are partly linked to their ability to alleviate pain sensations, similar to the effects of certain external opioids. They also influence the hypothalamic-pituitary-adrenal (HPA) axis, which is involved in the body’s stress response, potentially affecting the secretion of stress hormones like cortisol.
Enkephalins also have less prominent, but still significant, roles in other bodily functions. They can influence gut motility by altering neuronal excitability in the gastrointestinal tract. There is also evidence suggesting their involvement in immune system modulation, where they may act as immunostimulants at low concentrations, increasing the activity of certain immune cells. Furthermore, enkephalins contribute to neuroprotection by reducing toxicity and oxidative stress in the central nervous system, particularly in conditions like stroke, Alzheimer’s disease, or Parkinson’s disease.
Enkephalins and Health Conditions
The natural pain-relieving properties of enkephalins make them significant in pain management research. Scientists are exploring ways to target these endogenous opioids and their receptors to develop new strategies for pain relief.
Enkephalins also contribute to the body’s response to stress and injury. In situations of severe trauma, the rapid release and action of endogenous opioids, including enkephalins, can account for the temporary absence of pain. Research also indicates that enkephalin signaling is involved in stress resilience.