Morphine inhibitory effects

Bayer, B.M., Gastonguay, M.R., and Hernandez, M.C., Distinction between the in vitro and in vivo inhibitory effects of morphine on lymphocyte proliferation based on agonist sensitivity and naltrexone reversibility, Immunopharmacology, 23, 117, 1992. 

Opioids including morphine acting on metabotrobic pi—opioid receptors produce their inhibitory effect on cellular excitability in part by activation of Gj/0-protein-coupled K+ channels thereby hyperpolarizing the membrane potential (Williams et al., 1982 Han et al.,... 

Ikeda et al., 2000 Narita et al., 2000). KAtp channels have been shown to be opened by Gj/0-proteins (Edwards and Weston, 1993) and could thus mediate the inhibitory effect of morphine at the cellular level. Furthermore, such an interaction would also explain the antagonism and potentiation of morphine analgesia by Katp channel blockers and openers, respectively (see above). However, a recent electrophysiological study demonstrated that Katp channels do not mediate the effect of morphine in ventrolateral PAG neurones (Chiou and How, 2001). 

Tramadol has about one tenth the pain-relieving ability of morphine.53 There are two enantiomers, and both contribute to pain relief, but via different mechanisms. (+)-Tramadol and the metabolite (+)-0-desmethy 1-tramadol, which is referred to as Ml, are agonists of the mu opioid receptor. (+)-Tramadol inhibits serotonin reuptake and (-)-tramadol inhibits norepinephrine re uptake.25 This latter action enhances the inhibitory effects on pain transmission in the spinal cord. Because the actions of the two enantiomers are complementary, they are usually supplied as a racemic mixture. However, because it is a serotonin-reuptake blocker, interaction with other medications can lead to the occurrence of serotonin syndrome.54... 

The inhibitory response to morphine in this preparation is established as being due to an inhibition of acetylcholine release which Ca " " can reverse (35). We have been shown that the inhibitory effect of morphine on acetylcholine release can be reduced by elevating the Ca H concentration in the incubation bath (36). 

More recently, after allowing synaptosomes to reach a steady state Ca uptake in high Na+ medium (61), naloxone-reversible inhibition of basal Ca uptake by morphine and JB-endorphin could be consistently demonstrated (62,63) This inhibitory effect was noted only when ATP was present in milli-molar concentrations in the incubation medium. Efflux of Ca from preloaded synaptosomes was not significantly affected by morphine. The, inhibitory effect on Ca- "" " uptake was seen with synaptosomes prepared from frontal cortex, thalamus and hypothalamus, but not from the cerebellum, thus corresponding well with data on opiate receptor distribution (20,64). 

Inhibitory effect of nitric oxide (NO) synthase inhibitors on naloxone-precipitated withdrawal syndrome in morphine -dependent mice... 

Synthetic compounds, pentazocine and Darvon, which have morphine-like activity, and their effects on the pituitary-adrenocortical system. Morphine-like inhibitory effect on histamine ACTH-releasing action... 

Inhibitory effects of chronic administration of morphine on uridine and thymidine incorporating abilities of mouse liver and brain subcellular fractions... 

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