Morphine-related metabolites differentially activate adenylyl cyclase isozymes after acute and chronic administration.
(1/21)
Morphine-3- and morphine-6-glucuronide are morphine's major metabolites. As morphine-6-glucuronide produces stronger analgesia than morphine, we investigated the effects of acute and chronic morphine glucuronides on adenylyl cyclase (AC) activity. Using COS-7 cells cotransfected with representatives of the nine cloned AC isozymes, we show that AC-I and V are inhibited by acute morphine and morphine-6-glucuronide, and undergo superactivation upon chronic exposure, while AC-II is stimulated by acute and inhibited by chronic treatment. Morphine-3-glucuronide had no effect. The weak opiate agonists codeine and dihydrocodeine are also addictive. These opiates, in contrast to their 3-O-demethylated metabolites morphine and dihydromorphine (formed by cytochrome P450 2D6), demonstrated neither acute inhibition nor chronic-induced superactivation. These results suggest that metabolites of morphine (morphine-6-glucuronide) and codeine/dihydrocodeine (morphine/dihydromorphine) may contribute to the development of opiate addiction. (+info)
Nociceptin, endomorphin-1 and -2 do not interact with invertebrate immune and neural mu 3 opiate receptor.
(2/21)
AIM: To determine if endomorphin-1, -2 and nociceptin (orphanin FQ) bind to the mu 3 opiate receptor subtype or release nitric oxide as mu 3 selective ligands do. METHODS: These opioid peptides were examined for their ability to displace [3H]dihydromorphine (DHM) binding from the invertebrate (immunocytes and pedal ganglia) mu 3 opiate receptor in membrane homogenates. The ligands were also tested for their ability to release nitric oxide from the same intact tissues utilizing an amperometric probe that measures nitric oxide in real-time. RESULTS: Endomorphin-1, -2 and nociceptin do not displace [3H]DHM binding from immunocyte or pedal ganglia membrane homogenates nor do they release nitric oxide from these tissues. CONCLUSION: Since these newly discovered opioid peptides do not interact with the mu 3 opiate receptor subtype, endogenous morphine's significance is enhanced because it appears to be the only naturally occurring opiate ligand for the receptor. Furthermore, since this study involves invertebrate tissues, this signal system had to evolve early during evolution. (+info)
Contribution of dihydrocodeine and dihydromorphine to analgesia following dihydrocodeine administration in man: a PK-PD modelling analysis.
(3/21)
AIMS: It is not clear whether the analgesic effect following dihydrocodeine (DHC) administration is due to either DHC itself or its metabolite, dihydromorphine (DHM). We examined the relative contribution of DHC and DHM to analgesia following DHC administration in a group of healthy volunteers using a PK-PD link modelling approach. METHODS: A single oral dose of DHC (90 mg) was administered to 10 healthy volunteers in a randomised, double-blind, placebo-controlled study. A computerized cold pressor test (CPT) was used to measure analgesia. On each study day, the volunteers performed the CPT before study medication and at 1.25, 2.75, 4.25 and 5.75 h postdose. Blood samples were taken at 0.25 h (predose) and then at half hourly intervals for 5.75 h postdose. PK-PD link modelling was used to describe the relationships between DHC, DHM and analgesic effect. RESULTS: Mean pain AUCs following DHC administration were significantly different to those following placebo administration (P = 0.001). Mean pain AUC changes were 91 score x s(-1) for DHC and -17 score x s(-1) for placebo (95% CI = +/- 36.5 for both treatments). The assumption of a simple linear relationship between DHC concentration and effect provided a significantly better fit than the model containing DHM as the active moiety (AIC = 4.431 vs 4.668, respectively). The more complex models did not improve the likelihood of model fits significantly. CONCLUSIONS: The findings suggest that the analgesic effect following DHC ingestion is mainly attributed to the parent drug rather than its DHM metabolite. It can thus be inferred that polymorphic differences in DHC metabolism to DHM have little or no effect on the analgesic affect. (+info)
Reconstitution of high-affinity opioid agonist binding in brain membranes.
(4/21)
In synaptosomal membranes from rat brain cortex, the mu selective agonist [3H]dihydromorphine in the absence of sodium, and the nonselective antagonist [3H]naltrexone in the presence of sodium, bound to two populations of opioid receptor sites with Kd values of 0.69 and 8.7 nM for dihydromorphine, and 0.34 and 5.5 nM for naltrexone. The addition of 5 microM guanosine 5'-[gamma-thio]triphosphate (GTP[gamma S]) strongly reduced high-affinity agonist but not antagonist binding. Exposure of the membranes to high pH reduced the number of GTP[gamma-35S] binding sites by 90% and low Km, opioid-sensitive GTPase activity by 95%. In these membranes, high-affinity agonist binding was abolished and modulation of residual binding by GTP[gamma S] was diminished. High-affinity (Kd, 0.72 nM), guanine nucleotide-sensitive agonist binding was reconstituted by polyethylene glycol-induced fusion of the alkali-treated membranes with (opioid receptor devoid) C6 glioma cell membranes. Also restored was opioid agonist-stimulated, naltrexone-inhibited GTPase activity. In contrast, antagonist binding in the fused membranes was unaltered. Alkali treatment of the glioma cell membranes prior to fusion inhibited most of the low Km GTPase activity and prevented the reconstitution of agonist binding. The results show that high-affinity opioid agonist binding reflects the ligand-occupied receptor-guanine nucleotide binding protein complex. (+info)
Analgesia and serum assays of controlled-release dihydrocodeine and metabolites in cancer patients with pain.
(5/21)
Aim of the study was to assess dihydrocodeine (DHC) and metabolites concentrations and their correlations with DHC analgesia in cancer patients with pain. Thirty opioid-naive patients with nociceptive pain intensity assessed by VAS (visual analogue scale) > 40 received controlled-release DHC as the first (15 patients, 7 days) or as the second opioid (15 patients, 7 days). Blood samples were taken on day 2, 4 and 7 at each study period. DHC and its metabolites were assayed by HPLC. DHC provided satisfactory analgesia when administered as the first or the second opioid superior to that of tramadol. When DHC was the first opioid administered, DHC and dihydrocodeine-6-glucuronide (DHC-6-G) concentrations increased in the second and the third comparing to the first assay. A trend of nordihydromorphine (NDHM) level fall between the first and the third assay was noted; trends of dihydromorphine (DHM) level increase in the second relative to the first determination and decrease in the third compared to the second assay were observed. When DHC followed tramadol treatment a trend of DHC concentration increase in the second relative to the first assay was noted. DHC-6-G level increased in the second and in the third comparing to the first determination; NDHM and DHM concentrations were stable. DHC and DHC-6-G concentrations increased similarly during both treatment periods which suggest their prominent role in DHC analgesia. Few significant correlations were found between DHC dose, DHC and metabolites serum concentrations with analgesia suggesting the individual DHC dose titration. (+info)
Effects of nitrous oxide and halothane on mu and kappa opioid receptors in guinea-pig brain.
(6/21)
The effects of two general anesthetics, nitrous oxide and halothane, and oxygen on mu and kappa opioid receptor subtypes from guinea-pig brain were investigated. mu receptor binding was defined using [3H]dihydromorphine as the ligand. Nitrous oxide (100%) and halothane (2%) decreased the [3H]dihydromorphine binding affinity (Kdair = 0.87 nM, KdN2O = 1.45 nM, Kdhalothane = 2.30 nM) without affecting the density of binding sites. A decrease in the [3H]dihydromorphine binding affinity without influence on the density of binding sites was also observed in the presence of 100% oxygen (KdO2 = 1.40 nM). kappa receptor binding was defined using [3H](-)ethylketocyclazocine as the ligand, in the presence of 100 nM D-ala2-D-leu5-enkephalin and 30 nM morphine. While 100% nitrous oxide caused a slight decrease in [3H](-)ethylketocyclazocine binding affinity (Kdair = 0.24 nM, KdN2O = 0.31 nM) and a substantial decrease in the density of binding sites (Bmaxair = 115 fmol/mg protein, BmaxN2O = 84 fmol/mg protein), halothane dramatically affected both the affinity (Kdhalothane = 0.70 nM) and density (Bmaxhalothane = 38 fmol/mg protein). Oxygen (100%) reduced [3H]dihydromorphine binding affinity. Differential effects of two anesthetics on the same receptor or distinct actions of the same anesthetic on different receptors could indicate the presence of specific targets for anesthetics at the membrane level. Conversely, effects of volatile anesthetics on opioid receptors could reflect a non-specific perturbation of the lipidic and proteinaceous components of the membranes. (+info)
Further evidence that gonadal steroids do not modulate brain opiate receptors in male rats.
(7/21)
It is still unclear whether, in the male rat, castration and androgen replacement affect the binding characteristics of brain opiate receptors. To clarify this issue, the effects exerted by orchidectomy and testosterone (T) replacement on the subpopulation of brain mu opiate receptors were studied in male rats; testosterone was administered via subcutaneous Silastic capsules. Utilizing 3H-dihydromorphine (a mu receptor ligand) it has been shown that the affinity constant (Ka) of brain mu opiate binding sites, measured in plasma membrane preparations, is not affected by castration. When mu receptor concentrations were measured in individual brains, it was found that gonadectomy and T replacement failed to produce any change in the number of mu opiate receptors. These data suggest that, in male rats, gonadal steroids do not develop their central feedback effects by affecting brain mu opiate receptors. (+info)
Monoclonal anti-idiotypic antibodies to opioid receptors.
(8/21)
Two monoclonal anti-idiotypic antibodies (anti-Id-135 and anti-Id-14, both of the IgM class) which interact with the binding site of opioid receptors were generated. A monoclonal anti-beta-endorphin antibody (3-E7) which displays binding characteristics for opioid ligands similar to opioid receptors served as the antigen (Gramsch, C., Meo, T., Riethmuller, G., and Herz, A., (1983) J. Neurochem. 40, 1220-1226; Meo, T., Gramsch, C., Inan, R., Hollt, V., Weber, E., Herz, A., and Riethmuller, G. (1983) Proc. Natl. Acad. Sci. U.S.A. 80, 4048-4088) and the hybridomas obtained were screened for anti-idiotypic antibodies with Fab fragments of 3-E7. The anti-idiotypes were then screened for opioid binding to rat brain membrane receptors, yielding several positive clones two of which were more intensively studied. Both anti-idiotypic antibodies were about equally potent in displacing the mu- and delta-opioid receptor ligands [3H]dihydromorphine, 125I-labeled beta-endorphin, [D-Ala2, D-Leu5-3H]enkephalin and [3H]naloxone from rat brain membrane opioid receptors; no interaction was observed with the kappa-ligands [3H]ethylketazocine or [3H]bremazocine. The anti-idiotypic antibodies were able to precipitate [3H] diprenorphine binding sites from solubilized opioid receptor preparations. In addition, both antibodies showed opioid antagonistic properties as demonstrated by their abilities to block the inhibitory effect of [D-Ala2, D-Leu5-3H]enkephalin on prostaglandin E1-stimulated cAMP accumulation in NG 108-15 hybrid cells. Our findings demonstrate the successful generation of monoclonal antibodies interacting with membrane-bound and solubilized opioid receptors of the mu- and delta-type. (+info)