enkephalin--ala(2)-mephe(4)-gly(5)- and Acute-Disease

Clinical pain conditions may remain responsive to opiate analgesics for extended periods, but such persistent acute pain can undergo a transition to an opiate-resistant chronic pain state that becomes a much more serious clinical problem. To test the hypothesis that cellular mechanisms of chronic pain in the primary afferent also contribute to the development of opiate resistance, we used a recently developed model of the transition of from acute to chronic pain, hyperalgesic priming. Repeated intradermal administration of the potent and highly selective mu-opioid agonist, [d-Ala(2),N-MePhe(4),gly-ol]-enkephalin (DAMGO), to produce tolerance for its inhibition of prostaglandin E(2) hyperalgesia, simultaneously produced hyperalgesic priming. Conversely, injection of an inflammogen, carrageenan, used to produce priming produced DAMGO tolerance. Both effects were prevented by inhibition of protein kinase Cepsilon (PKCepsilon). Carrageenan also induced opioid dependence, manifest as mu-opioid receptor antagonist (d-Phe-Cys-Tyr-d-Trp-Orn-Thr-Pen-Thr-NH(2))-induced hyperalgesia that, like priming, was PKCepsilon and G(i) dependent. These findings suggest that the transition from acute to chronic pain, and development of mu-opioid receptor tolerance and dependence may be linked by common cellular mechanisms in the primary afferent.

Topics: Acute Disease; Analgesics, Opioid; Animals; Carrageenan; Chronic Disease; Drug Tolerance; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; GTP-Binding Protein alpha Subunits, Gi-Go; GTP-Binding Protein alpha Subunits, Gs; Hyperalgesia; Inflammation; Male; Nociceptors; Opioid-Related Disorders; Pain; Protein Kinase C-epsilon; Rats; Rats, Sprague-Dawley; Receptors, Opioid, mu; Signal Transduction; Substance Withdrawal Syndrome

The detrimental impact of opioid agonist on the clinical management of inflammatory diseases remains elusive. Given the anti-inflammatory properties of the mu-opioid receptor (MOR) agonists at the intestinal barrier, we hypothesised that MOR activation might also dampen acute hepatic inflammation and cell death-major determinants in the pathogenesis of liver diseases.. The expression of MOR in liver biopsy specimens and peripheral blood mononuclear cells of untreated patients with chronic hepatitis C virus infection and controls, primary hepatocytes and cell lines was determined by quantitative PCR, immunoblotting and/or immunohistochemistry. The effects of peripheral MOR agonist (d-Ala2,NMe-Phe4,Gly5-ol (DAMGO)) and/or antagonist (naloxone methiodide) were explored in two models of acute hepatitis in mice. MOR-deficient mice were used to evaluate the essential regulatory role of MOR during carbon tetrachloride (CCl(4))-induced hepatitis. The role of DAMGO in cell death was investigated using terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling (TUNEL) analysis and quantification of lactate dehydrogenase release.. The key role of MOR in the prevention of acute hepatic inflammation and cell death in vivo and in vitro is reported. Whereas MOR gene expression increased transiently in the model of acute liver injury and TNFalpha-treated HepG2 cells, an impaired expression of MOR mRNA in human chronic hepatitis C samples was found. Furthermore, preventive administration of the selective MOR agonist DAMGO enhanced hepatoprotective-signalling pathways in vivo that were blocked by using naloxone methiodide. Consistently, genetic and pharmacological inhibition of MOR enhanced the severity associated with experimental hepatotoxin-induced hepatitis. Finally, treatment with DAMGO was shown to prevent cell death in vitro in HepG2 cells in a MOR-dependent manner and to prevent concanavalin A- and CCl(4)-induced cell death in vivo, providing a possible explanation for the anti-inflammatory role of MOR activation in the liver.. The results indicate that MOR agonists may prevent acute hepatitis and hold promising therapeutic use to maintain remission in both chronic inflammatory bowel and liver diseases.

Topics: Acute Disease; Animals; Biopsy; Carbon Tetrachloride; Cell Death; Concanavalin A; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Gene Expression; Hepatitis; Hepatitis C, Chronic; Hepatitis, Animal; Hepatocytes; Humans; Male; Mice; Mice, Inbred BALB C; Mice, Inbred C57BL; Receptors, Opioid, mu; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Tumor Cells, Cultured; Tumor Necrosis Factor-alpha; Up-Regulation

In the present work the effect of papaverine, a non specific smooth muscle relaxant, was investigated on the naloxone-precipitated withdrawal contracture of the acute morphine-dependent guinea-pig ileum in vitro. Furthermore, the effect of papaverine was also considered on DAGO (highly selective mu -agonist) and U50-488H (highly selective k-agonist) withdrawal to test whether the possible interaction of papaverine on opioid withdrawal involves mu - and/or k-opioid receptors. Following a 4 min in vitro exposure to opioid agonist, the guinea-pig isolated ileum exhibited a strong contracture after the addition of naloxone. Papaverine treatment (1 x 10(-7) - 5 x 10(-7) - 1 x 10(-6) M) before or after the opioid agonists was able of both preventing and reversing the naloxone-induced contracture after exposure to mu (morphine and DAGO) or k (U50-488H) opiate agonists in a concentration-dependent fascion. Both acetylcholine response and electrical stimulation were not affected by papaverine treatment whereas the final opiate withdrawal was still reduced. The results of the present study indicate that papaverine was able to produce significative influence on the opiate withdrawal in vitro and papaverine was able to exert its effect both at mu and k opioid agonists.

Topics: 3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; Acute Disease; Animals; Dose-Response Relationship, Drug; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Guinea Pigs; Ileum; Male; Morphine; Muscle Contraction; Muscle, Smooth; Narcotic Antagonists; Papaverine; Parasympatholytics; Phytotherapy; Plants, Medicinal; Receptors, Opioid; Substance Withdrawal Syndrome

The endogenous synthesis of morphine has been clearly demonstrated throughout the phylogenesis of the nervous system of mammals and lower animals. Endogenous morphine, serving as either a neurotransmitter or neurohormone, has been demonstrated in the nervous system of both vertebrates and invertebrates. As one of the effects of exogenous morphine is the modulation of pain perception, we investigated the effects that the depletion of endogenous morphine had on nociceptive transmission. The immunoneutralization of endogenous morphine from brain extracellular spaces was obtained through the intracerebroventricular administration of affinity purified anti-morphine IgG to mice, which then underwent the hot plate test. Endogenous morphine immunoneutralization decreased thermal response latency and attenuated the anti-nociceptive effect of the mu selective agonist DAMGO in hot plate test suggesting that endogenous morphine is involved in pain modulation.

Topics: Acute Disease; Analgesics, Opioid; Animals; Buffers; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalin, D-Penicillamine (2,5)-; Ethylketocyclazocine; Gas Chromatography-Mass Spectrometry; Hyperalgesia; Immunoglobulin G; Injections, Intraventricular; Male; Mice; Mice, Inbred Strains; Morphine; Motor Activity; Nociceptors; Opioid Peptides; Skin Temperature

We studied spinal analgesic and antiallodynic effects of endomorphin-1 and endomorphin-2 administered i.t. in comparison with Tyr-D-Ala-Gly-MePhe-Gly-ol (DAMGO) or morphine, during acute, inflammatory and neuropathic pain in rats chronically implanted with intrathecal cannulas. Endomorphin-1 and endomorphin-2 (2.5, 5, 10 microg i.t.) increased the tail-flick latency and, to the lesser extent, the paw pressure latency. The range of potencies in both those models of acute pain was as follows: DAMGO > morphine = endomorphin-1 > endomorphin-2. In a model of inflammatory pain, the number of formalin-induced flinching episodes was decreased by endomorphin-1. The effect of endomorphin-2 was much less pronounced. Both DAMGO and morphine significantly inhibited the pain-related behavior evoked by formalin. In a neuropathic pain model (sciatic nerve crushing in rats), endomorphin-1 and -2 (5 microg i.t.) had a statistically significant effect on the tail-flick latency and on the cold-water tail flick latency. Morphine, 5 microg, was found to be ineffective. Endomorphin-1 and -2 (2.5 and 5 microg i.t.) dose-dependently antagonized allodynia. Those effects of endomorphins were antagonized in acute (30 microg), inflammatory (30 microg) and neuropathic pain models (60 microg) by cyprodime, a selective mu-opioid receptor antagonist. In conclusion, our results show a strong analgesic action of endomorphins at the spinal cord level. The most interesting finding is a strong, stronger than in the case of morphine, antiallodynic effect of endomorphins in rats subjected to sciatic nerve crushing, which suggests a possible use of these compounds in a very difficult therapy of neuropathic pain.

Topics: Acute Disease; Analgesics, Opioid; Animals; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalins; Inflammation; Injections, Spinal; Male; Morphine; Pain; Rats; Spinal Cord

Topics: Acute Disease; Animals; Anti-Arrhythmia Agents; Arrhythmias, Cardiac; Cats; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalins; Female; Male; Myocardial Ischemia; Nerve Fibers, Myelinated; Receptors, Opioid, mu; Vagotomy; Vagus Nerve

To obtain data on the degree to which the opioid system is changed in cholestasis, endogenous opioid activity in plasma of rats with acute cholestasis was determined 5 days after bile duct resection. Total plasma opioid activity was determined using a radioreceptor technique that measured the displacement of the opiate receptor ligand [3H]-DAMGO from lysed synaptosomal fractions of normal rat brain. Plasma total opioid activity was threefold greater in bile duct-resected rats than in sham-operated and unoperated controls (P less than or equal to 0.05). Plasma levels of the individual endogenous opioid, methionine-enkephalin, were determined using a sensitive radioimmunoassay, and the specificity of the assay was confirmed using high-performance liquid chromatography. In cholestatic rats, plasma methionine-enkephalin levels were more than six-fold greater than in sham-operated controls (P less than or equal to 0.001) and more than 17-fold greater than in unoperated controls (P less than or equal to 0.001). However, plasma methionine-enkephalin levels accounted for less than 5% of total plasma opioid activity after bile duct resection. Plasma methionine-enkephalin levels in both cholestatic plasma and plasma from sham-operated animals were stable when incubated in vitro despite the presence of undiminished activity of the major enkephalin-degrading enzymes. Thus, protection of methionine-enkephalin from degradation may be a factor contributing to the elevated plasma levels of methionine-enkephalin found in cholestasis. The magnitude of the increase in plasma endogenous opioid activity in bile duct-resected rats provides support for the hypothesis that endogenous opioids contribute to the pathophysiology of cholestasis.

Topics: Acute Disease; Amino Acid Sequence; Aminopeptidases; Animals; Cholestasis; Disease Models, Animal; Endorphins; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalin, Methionine; Enkephalins; Male; Molecular Sequence Data; Rats; Rats, Inbred Strains

The experiments have been performed on 93 male rats, weighing 200-250 g. In acute blood loss various arterial pressure (AP) changes have been demonstrated--the marked hypertension is being changed by gradual AP increase. The injection of m-receptors' agonist DAGO prevents systolic and diastolic AP increase, agonist DADL prevents diastolic AP increase in acute momentary blood loss. In gradual blood loss DAGO (more than DADL) slows down both the decrease and the subsequent AP increase in rats. DAGO is determined to decrease, and DADL--to increase the minute blood volume. The mechanisms of opioids' action and their significance in pathogenesis of hemodynamic disturbances in shock are being discussed.

Topics: Acute Disease; Animals; Drug Evaluation, Preclinical; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalin, Leucine; Enkephalin, Leucine-2-Alanine; Enkephalins; Hemodynamics; Hemorrhage; Male; Rats; Rats, Inbred Strains; Receptors, Opioid; Shock, Hemorrhagic; Time Factors

Topics: Acute Disease; Animals; Cerebral Ventricles; Chronic Disease; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalins; Injections, Intraperitoneal; Injections, Intraventricular; Male; Mice; Mice, Inbred ICR; Pain