Opioid system endorphins

In addition to the weU-defined opioid systems in the central nervous system, the three opioid peptides and their precursor mRNA have also been identified in peripheral tissues. ( -Endorphin is most abundant in the pituitary, where it exists in corticotroph cells with ACTH in the anterior lobe and in melanotroph cells with MSH in the intermediate lobe (59). Enkephalin and pre-pro-enkephalin mRNA have been identified in the adrenal medulla (60) and this has been the source of material for many studies of pro-enkephalin synthesis and regulation. Pre-pro-enkephalin mRNA has also been identified in the anterior and posterior lobes of the pituitary (61). mRNA for all three opioid precursors has been identified in the reproductive system (62—64). POMC... 

Additionally, an opioid antagonist, naltrexone, has been used to treat children with autism. The results from these studies have been mixed, with some studies showing a mild decrease in hyperactivity and self-injurious behavior, and improved attention (Gillberg, 1995). The children who respond best to this medication appear to have more severe abnormalities in their beta endorphin levels (Bouvard et al., 1995). Overall, the research suggests that the endogenous opioid system, which is important in the reward aspects of affiliation, may also play a role in the neurobiology of autism. 

It is justified to assume that cholestatis-related pruritus is caused by substances that are normally excreted in the bile. Nevertheless, it has not been possible to detect a specific causative substance up to now. Under experimental and clinical conditions, raised bile acid levels in the serum or in the skin are found both with and without pruritus - but no adequate correlation could be established. Recent findings point to an increased tonus of the opioid system in the CNS (endorphins) as being of prime importance in the pathogenesis of cholestasis-related pruritus. Endogenous lipophilic bile acids possibly effect the release of hitherto unknown prurito-... 

Previous reports of opioid withdrawal on single exposure have been described after the administration of intramuscular morphine in healthy individuals. This case suggests that opioid dependence can occur after acute exposure to morphine by the epidural route too. An alternative explanation (28) is that the stress of labor may have led to increased endogenous opioid activity, particularly B-endorphin, and that the antagonistic effect of naloxone on the endogenous opioid system contributed to the clinical effects in this patient. Moreover, the authors pointed out that many symptoms characteristic of the classic opioid withdrawal sjmdrome were not present in the patient. 

Fig. 24.2. Location of endogenous opioid nerve tracts in the central nervous system. Endorphins and opioid receptors in the dorsal horn of the spinal cord, thalamus, and periaqueductal gray (PAG) areas are associated with the transmission of pain signals.

The work flow for dPLIMSTEX starts with half the volume of an equilibrated protein-peptide complex for measurement. The other half is diluted in aqueous buffer before incubation (Figure 11.5). The dilution step is continued until the concentration of the peptide is too low to be detected. dPLIMSTEX was first demonstrated by using a model system, calcium-saturated calmodulin with the opioid peptide )-endorphin it yielded a similar binding constant as that determined by standard PLIMSTEX and other methods. dPLIMSTEX was then applied to a monoclonal antinitro-tyrosine antibody, in complex with a 3-nitrotyrosine-modified peptide system. A binding stoichiometry of 1 2 was confirmed. In addition, a in the low nM range and a minimum of five amino... 

Mizoguchi, H., Tseng, L. F., Suzuki, T., Sora, I. and Narita, M. Recent advances in the search for the p-opioidergic system differential mechanism of g-protein activation induced by endogenous p-opioid peptides, endomorphin and 5-endorphin. Jpn. J. Pharmacol. 89 239-244, 2002. 

The body modulates pain through several processes. The endogenous opiate system consists of neurotransmitters (e.g., enkephalins, dynorphins, and /1-endorphins) and receptors (e.g., fl, S, k) that are found throughout the CNS. Endogenous opioids bind to opioid receptors and modulate the transmission of pain impulses. 

The classic endogenous opioid peptides are derived from one of three families of precursors proopiomelanocortin (POMC), pro-dynorphin, and pro-enkephalin. Many active opioid peptides are derived from these three, but the best known are )S-endorphin, enkephalin, and dynorphin. POMC is produced by nuclei in the hypothalamus and medulla (Khachaturian et al. 1985 Watson et al. 1978 Bloom et al. 1978). Enkephalin and dynorphin neurons are distributed to all levels of the central nervous system (Hokfelt et al. 1977 Khachaturian et al. 1983 Sar et al. 1978 Khachaturian et al. 1985). 

The most potent and pervasive pain suppression system appears to be provided by endogenous opioids, particularly methionine encephalin and beta endorphin. These opioids and their receptors are widely distributed at several levels in the central nervous system (Mansour et al., 1988). Enkephalins appear to control the responses of dorsal horn neurons and may also modulate pain... 

The causes and mechanisms of chronic pain syndromes are diverse (Lance 8c McLeod, 1981). A similarity with depression has been noted by several authors and it has been suggested that chronic pain syndromes might result from reduced activity in serotonergic systems involved in pain suppression and mood control (Moldofsky, 1982). Other authors have suggested that a causative factor in chronic pain syndromes might be abnormally low concentrations or activity of endogenous opioids, particularly beta-endorphin (Lip-man et al., 1990). 

Marked changes in physiological functions can occur if naloxone is given when the endorphin system has been modified by opioids. Following the use of naloxone, a reduced plasma prolactin concentration was noted (737). 

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