Peripheral nervous system opioid effects

Opioid drugs act at opioid receptors distributed throughout the central/peripheral nervous system, causing a wide range of physiological, behavioural and cognitive effects. The main adverse drug interactions are due to additive depressive effects on the CNS, which results in loss of consciousness, respiratory depression and hypotension. 

Peripheral nervous system. The discovery of opioid receptors is sensory nerves and their inhibiting effect on inflammatory mediators may lead to advances in pain control. 

Opioid-induced analgesia is produced through the action of opioid receptors on presynaptic terminals of the C-fibers and A-delta fibers. These fibers, which transmit nociceptive messages, are inhibited by the indirect effects of opioids, which in turn reduce the release of neurotransmitters such as substance P, CGRP, and glutamate. This effect occurs in the peripheral nervous system as well as at the primary afferent terminals in the spinal cord. 

Fecho, K. et al., Assessment of the involvement of central nervous system and peripheral opioid receptors in the immunomodulatory effects of acute morphine treatment in rats, J. Pharmacol. Exp. Ther., 276, 626, 1996a. 

The opioids may modulate the actions of the immune system by effects on lymphocyte proliferation, antibody production, and chemotaxis. Natural killer cell cytolytic activity and lymphocyte proliferative responses to mitogens are usually inhibited by opioids. Although the mechanisms involved are complex, activation of central opioid receptors could mediate a significant component of the changes observed in peripheral immune function. In general, these effects are mediated by the sympathetic nervous system in the case of acute administration and by the hypothalamic-pituitary-adrenal system in the case of prolonged administration of opioids. 

Subsequently, numerous peptides with opioid-like effects have been found in the central nervous system and in peripheral tissues. These endogenous opioid peptides vary in size, but their amino terminals mostly share a similar enkephalin sequence of amino acids. Currently, four separate, individually gene-derived families of endogenous opioid peptides are recognized the endorphins, the enkephalins, the dynorphins and the endomorphins [17a], -Endorphin interacts predominantly with n and 6 receptors, Leu-enkephalin and Met-enkephalin interact predominantly with 5 receptors, dynorphin shows preference for k receptors [17b], while endomorphins 1 and 2 exhibit... 

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