Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UNIPROT:P01189 (beta-endorphin)
 21,003 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

It is well documented that the mu-opioid receptor (MOP-R) is expressed by neurons in several central nervous system regions. Its occupancy with agonist drugs modulate a variety of physiological processes including pain, reward, stress, immune responses, neuroendocrine functions, and cardiovascular control. Based on the receptor binding assay, endomorphin-1 and endomorphin-2 have the highest specificity and affinity for the MOP-R of any endogenous substance so far described in the mammalian nervous system. In contrast, beta-endorphin exhibits the strongest actions among endogenous opioid peptides mainly through the MOP-R; however, it also shows the distinct pharmacological actions. Recent cloning and expression studies have indicated that MOP-Rs are seven-transmembrane domain receptors whose actions are mediated through activation of heterotrimeric guanine nucleotide binding proteins (G-proteins). The activation of G-proteins by MOP-Rs can be measured by assessing agonist-induced stimulation of membrane binding of guanosine-5'-o-(3-[35S]thio)triphosphate ([35S]GTPgammaS). The subject of the present review is to focus on the differential mechanism underlying G-protein activation induced by these mu-opioid peptides using the [35S]GTPgammaS binding assay.
 ...
PMID:Differential mechanism of G-protein activation induced by endogenous mu-opioid peptides, endomorphin and beta-endorphin. 1218 27

In this study, we investigated the effects of acute morphine administration, chronic intermittent escalating-dose morphine administration and spontaneous withdrawal from chronic morphine on mRNA levels of mu opioid receptor (MOP-r), and the opioid peptides pro-opiomelanocortin (POMC) and preprodynorphin (ppDyn) in several key brain regions of the rat, associated with drug reward and motivated behaviors: lateral hypothalamus (lat.hyp), nucleus accumbens (NAc) core, amygdala, and caudate-putamen (CPu). There was no effect on MOP-r mRNA levels in these brain regions 30 min after either a single injection of morphine (10 mg/kg, i.p.) or chronic intermittent escalating-dose morphine (from 7.5 mg/kg per day on day 1 up to 120 mg/kg per day on day 10). Activation of the stress-responsive hypothalamic-pituitary-adrenal axis by 12 h withdrawal from chronic morphine was confirmed; both POMC mRNA levels in the anterior pituitary and plasma adrenocorticotropic hormone levels were significantly elevated. Under this withdrawal-related stress condition, there was an increase in MOP-r mRNA levels in the lat.hyp, NAc core, and CPu. Recent studies have demonstrated a novel role for the lat.hyp orexin (or hypocretin) activation in both drug-related positive rewarding, and withdrawal effects. Around 50% of lat.hyp orexin neurons express MOP-r. Therefore, we also examined the levels of lat.hyp orexin mRNA, and found them increased in morphine withdrawal, whereas there was no change in levels of the lat.hyp ppDyn mRNA, a gene coexpressed with the lat.hyp orexin. Our results show that there is an increase in MOP-r gene expression in a region-specific manner during morphine withdrawal, and support the hypothesis that increased lat.hyp orexin activity plays a role in morphine-withdrawal-related behaviors.
 ...
PMID:Mu opioid receptor and orexin/hypocretin mRNA levels in the lateral hypothalamus and striatum are enhanced by morphine withdrawal. 1706 97

Phosphorylation of specific sites in the second intracellular loop and in the C-terminal domain have previously been suggested to cause desensitization and internalization of the mu-opioid receptor (MOP-R). To assess sites of MOP-R phosphorylation in vivo, affinity-purified, phosphoselective antibodies were raised against either phosphothreonine-180 in the second intracellular loop (MOR-P1) or the C-terminal domain of MOP-R containing phosphothreonine-370 and phosphoserine-375 (MOR-P2). We found that MOR-P2-immunoreactivity (IR) was significantly increased within the striatum of wild-type C57BL/6 mice after injection of the agonist fentanyl. Pretreatment with the antagonist naloxone blocked the fentanyl-induced increase. Furthermore, mutant mice lacking MOP-R showed only non-specific nuclear MOR-P2-IR before or after fentanyl treatment, confirming the specificity of the MOR-P2 antibodies. To assess whether MOP-R phosphorylation occurs following endogenous opioid release, we induced chronic neuropathic pain by partial sciatic nerve ligation (pSNL), which caused a significant increase in MOR-P2-IR in the striatum. pSNL also induced signs of mu opioid receptor tolerance demonstrated by a rightward shift in the morphine dose response in the tail withdrawal assay and by a reduction in morphine conditioned place preference (CPP). Mutant mice selectively lacking all forms of the beta-endorphin peptides derived from the proopiomelanocortin (Pomc) gene did not show increased MOR-P2-IR, decreased morphine antinociception, or reduced morphine CPP following pSNL. In contrast gene deletion of either proenkephalin or prodynorphin opioids did not block the effects of pSNL. These results suggest that neuropathic pain caused by pSNL in wild-type mice activates the release of the endogenous opioid beta-endorphin, which subsequently induces MOP-R phosphorylation and opiate tolerance.
 ...
PMID:The absence of endogenous beta-endorphin selectively blocks phosphorylation and desensitization of mu opioid receptors following partial sciatic nerve ligation. 1746 16

The mu-opioid receptor encoded by the gene OPRM1 plays a primary role in opiate, alcohol, cocaine and nicotine addiction. Studies using opioid antagonists demonstrate that the mu-opioid receptor (MOP-r) also mediates the hypothalamic-pituitary-adrenal (HPA) axis stress response. A common polymorphism in exon one of the MOP-r gene, A118G, has been shown to significantly alter receptor function and MOP-r gene expression; therefore, this variant likely affects HPA-axis responsivity. In the current study, we have investigated whether the presence of the 118AG variant genotype affects HPA axis responsivity to the stressor metyrapone, which transiently blocks glucocorticoid production in the adrenal cortex. Forty-eight normal and healthy volunteers (32 men, 16 women) were studied, among whom nine men and seven women had the 118AG genotype. The 118G allele blunted the adrenocorticotropic hormone (ACTH) response to metyrapone. Although there was no difference in basal levels of ACTH, subjects with the 118AG genotype had a more modest rise and resultant significantly lower ACTH levels than those with the prototype 118AA at the 8-hour time point (P < 0.02). We found no significant difference between genders. These findings suggest a relatively greater tonic inhibition at hypothalamic-pituitary sites through the mu-opioid receptor and relatively less cyclical glucocorticoid inhibition in subjects with the 118G allele.
 ...
PMID:Mu-opioid receptor A118G polymorphism in healthy volunteers affects hypothalamic-pituitary-adrenal axis adrenocorticotropic hormone stress response to metyrapone. 2150 51