BACKGROUND: Analgesic tolerance to opioids has been described in both experimental and clinical conditions, which may limit their clinical utility. This study investigated the effects of intrathecal adenosine A1 receptor agonist (R-PIA) on spinal morphine tolerance. METHODS: SD rats were given intrathecal injections of saline 10microliter, R-PIA 10microgram, morphine 10microgram, or R-PIA plus morphine combinations for 7 days (R-PIA given for days 1-7; days 1-3; or days 5-7). Antiallodynic testing using von Frey filaments was carried out before and 30 minutes after the drug injection. On day 8, an antiallodynic dose-response curve was constructed and the 50% effective dose (ED(50)) for morphine (given alone) was calculated for each study group. RESULTS: The coinjection group of R-PIA with morphine blocked the development of tolerance, as shown by the preservation of morphine antiallodynia over 7 days the concomitant decrease in the ED(50) values on day 8, compared with the morphine-alone group. Although additive analgesia over days 1-7 cannot be ruled out, the reductions of the ED(50) in the R-PIA and morphine combination group suggest some suppression of tolerance. CONCLUSIONS: These results suggest that intrathecal R-PIA prevents the development of spinal opioid tolerance. Future studies will be needed to examine the respective roles of supraspinal and peripheral sites of R-PIA and morphine interaction, and to investigate the mechanisms underlying the action of R-PIA on opioid tolerance.
Adenosine A1 Receptor Agonists* ; Adenosine* ; Analgesia ; Analgesics, Opioid ; Animals ; Hyperalgesia ; Injections, Spinal ; Models, Animal* ; Morphine* ; Pain, Postoperative* ; Rats* ; Receptor, Adenosine A1*

BACKGROUND: A Nerve ligation injury may produce a pain syndrome that includes tactile allodynia. Reversal effects on tactile allodynia have been demonstrated after an intrathecal administration of adenosine analogues or morphine. Adenosine receptor agonists have been known to have antinociceptive and antiallodynic effects in many animal and human studies. We examined the drug interactions between morphine and adenosine agonists in a rat model of a nerve ligation injury. METHODS: Male Sprague Dawley rats were prepared with a tight ligation of the left lumbar 5 th and 6 th spinal nerves and chronic lumbar intrathecal catheter implantation for drug administration. We measured the tactile allodynia by applying von Frey filaments ipsilateral to the lesioned hindpaw. Thresholds for paw withdrawal were assessed. Morphine (1 - 30ng), adenosine (1 - 30ng) and R-PIA (0.1 - 10ng) were administered to obtain the dose-response curves and the 50% effective dose (ED50). Fractions of ED50 values were administered to establish the ED50 of drug combinations. Drug interactions were evaluated by the fractional and isobolographic analyses. Allodynic thresholds for left lesioned hindpaw withdrawal to the von Frey hairs test were assessed and converted to % maximal possible effect (%MPE). RESULTS: The antiallodynic effect of morphine, adenosine, and R-PIA were produced in a dose dependent manner. The antiallodynic effects of combinations showed a similar pattern. Isobolographic analysis revealed a synergistic interaction for the morphine-R-PIA combination but not for the morphine-adenosine combination. However, fractional analysis produced a synergistic result for two combination groups. CONCLUSIONS: The results demonstrated that intrathecal co-administration of adenosine A1 receptors agonist and morphine showed the synergistic effect on nerve ligation injury induced allodynia.
Adenosine* ; Animals ; Catheters ; Drug Combinations ; Drug Interactions ; Hair ; Humans ; Hyperalgesia ; Injections, Spinal ; Ligation* ; Male ; Models, Animal ; Morphine* ; Purinergic P1 Receptor Agonists* ; Rats* ; Rats, Sprague-Dawley ; Receptor, Adenosine A1 ; Receptors, Purinergic P1* ; Spinal Nerves

OBJECTIVE: To investigate the changes of myocardial protein expression profiles in 2-chloro-N6-cyclopentyladenosine (CCPA), an adenosine A1 receptor agonist-induced delayed myocardial protection in New Zealand rabbits . METHODS: A total of 8 rabbits were randomly divided into a CCPA group (CCPA group) and a normal saline group (NS group). CCPA and NS were infused into rabbits in the CCPA group and the NS group respectively. Twenty-four hours later, the rabbits were subjected to 30 min left anterior descending coronary artery occlusion and were reperfused for 2 hours, then the ischemic zone tissues of left ventricle were sampled for proteomic analysis.A total of 12 other New Zeland rabbits were divided into a sham group (Sham group), a normal saline group (NS group) and a CCPA group (CCPA group). The expression of αB-crystalline, one of the differential proteins, was confirmed by Western blot. RESULTS: Analysis of two dimensional gel electrophoresis showed that the expression of 55 protein spots were different between the two groups, 17 protein spots were preliminarily identified with the matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) and Mascot and Expasy bioinformatics software. These proteins included stress proteins, metabolism-associated proteins, signal transduction pathway-related proteins, ionophorous proteins, immunity-associated proteins, and so on. Western blot showed that the expression of αB-crystalline was significantly up-regulated in the CCPA group. CONCLUSION The myocardial protein expression profiles are changed markedly in the preconditioning late phase of CCPA .The differential proteins might be involved in the delayed cardioprotection induced by CCPA.
Adenosine ; analogs & derivatives ; therapeutic use ; Adenosine A1 Receptor Agonists ; therapeutic use ; Animals ; Female ; Ischemic Postconditioning ; methods ; Male ; Myocardial Reperfusion Injury ; metabolism ; prevention & control ; Myocardium ; metabolism ; Proteome ; analysis ; Proteomics ; methods ; Rabbits

OBJECTIVETo investigate the effects of injecting adenosine A1 receptor agonist (CCPA) into Baihui (GV20) on the cerebral cortex induced by the ischemia/reperfusion of middle cerebral artery occlusion (MCAO) in rats.

METHODSTwenty-four SD rats were randomly divided into four groups, i. e., the sham-operation group, the model group, the DMSO group, and the CCPA group. The MCAO model was established by thread embolism method. At the moment of ischemia/reperfusion, the rats in DMSO group and the CCPA group were injected with DMSO (20 microL) and CCPA (0.1 mmol) 20 microL into Baihui respectively. The rats' behavior, the histomorphology of ischemic penumbra in the cerebral cortex, the expressions of Bcl-2 protein, and the apoptosis rate of neurocytes were assessed.

RESULTSCompared with the model group and the DMSO group, the rats' behavior were markedly improved in the CCPA group (P<0.05). No obvious karyopyknosis and cytoplasm empty dye of neurons appeared. The Bcl-2 expressions in rats' cerebral cortex obviously increased (P<0.01). The apoptosis number of neurons obviously decreased (P<0.01).

CONCLUSIONSInjecting CCPA into Bahui improved the rats' behavior and histomorphology in the ischemic penumbra, elevated the expressions of Bcl-2 protein, and reduced the neurons apoptosis rate in the ischemic penumbra. It alleviated the cerebral ischemia-reperfusion injury. Therefore, it could be taken as a new treatment method.

Acupuncture Points ; Adenosine A1 Receptor Agonists ; administration & dosage ; pharmacology ; therapeutic use ; Animals ; Brain Ischemia ; metabolism ; therapy ; Cerebral Cortex ; drug effects ; metabolism ; Male ; Rats ; Rats, Sprague-Dawley ; Reperfusion Injury ; metabolism ; therapy