Endomorphins are naturally occurring opioid peptides found within the body, involved in regulating pain and mood. These substances are a subject of ongoing scientific investigation due to their specific actions and potential therapeutic applications. Their discovery has enhanced understanding of how the body manages pain and emotional states.
What Are Endomorphins
Endomorphins are endogenous opioid peptides that interact with opioid receptors. They were first identified in 1997 by James Zadina, Abba Kastin, and their colleagues. There are two types: Endomorphin-1 and Endomorphin-2.
These peptides are small, classified as tetrapeptides. Endomorphin-1 has the sequence Tyr-Pro-Trp-Phe, while Endomorphin-2 consists of Tyr-Pro-Phe-Phe. This structural specificity enables endomorphins to bind with high affinity and selectivity to the mu-opioid receptor.
Endomorphin-1 is found predominantly in the brain and upper brainstem, while Endomorphin-2 is largely concentrated in the spinal cord and lower brainstem. Their presence in both the central and peripheral nervous systems suggests they influence various bodily functions.
How Endomorphins Function
Endomorphins function as pain modulators due to their selective binding to mu-opioid receptors. When endomorphins bind to these receptors, they induce inhibitory effects on neuronal activity, which contributes to pain relief. This analgesic effect is similar to that produced by morphine, which also targets the mu-opioid receptor.
In the peripheral nervous system, endomorphins reduce pain by inhibiting the release of substance P, a neurotransmitter involved in transmitting pain signals. In the central nervous system, endomorphins suppress the release of gamma-aminobutyric acid (GABA), an inhibitory neurotransmitter. This suppression leads to an increase in dopamine production, which is associated with feelings of pleasure and reward, further contributing to their pain-relieving effects.
Beyond pain, endomorphins are also involved in other physiological processes. Their distribution in various parts of the central and peripheral nervous systems suggests roles in stress response, mood regulation, and functions like reward and arousal. While pain modulation is their most well-understood function, ongoing research continues to explore their broader impact.
Endomorphins Versus Endorphins
While their names sound similar, endomorphins and endorphins are distinct endogenous opioid systems with differences in their chemical structure, receptor binding, and physiological roles. Endorphins, a broader class of endogenous opioid peptides, were discovered earlier, with enkephalins being isolated in 1973 and the term “endorphin” later coined to describe any peptide with morphine-like activity. Endomorphins, on the other hand, were identified much more recently in 1997.
A key distinction lies in their chemical makeup. Endomorphins are tetrapeptides, meaning they consist of four amino acids, with specific sequences like Tyr-Pro-Trp-Phe for Endomorphin-1 and Tyr-Pro-Phe-Phe for Endomorphin-2. In contrast, endorphins, such as beta-endorphin, are much longer chains of amino acids; beta-endorphin, for example, contains 31 amino acids. This difference in length and specific amino acid sequence contributes to their varied interactions within the body.
The primary difference in their receptor binding lies in their selectivity. Endomorphins exhibit high affinity and remarkable selectivity exclusively for the mu-opioid receptor. Endorphins, while also binding to mu-opioid receptors, can interact with other opioid receptor types, including delta and kappa receptors, though beta-endorphin shows a strong preference for mu-receptors. This specialized binding profile of endomorphins is a significant characteristic.
Regarding their distribution and roles, Endomorphin-1 is concentrated in the brain and upper brainstem, while Endomorphin-2 is mainly found in the spinal cord and lower brainstem. Endorphins, particularly beta-endorphin, are produced in the pituitary gland and hypothalamus and are released into both the central and peripheral nervous systems in response to pain or stress. While both contribute to pain relief, the specific mechanisms and broader physiological impacts of these distinct systems continue to be areas of active research.