Effects of dezocine on morphine tolerance and opioid receptor expression in a rat model of bone cancer pain.

BACKGROUND: Clinically, the coadministration of opioids to enhance antinociception and decrease tolerance has attracted increasing research attention. We investigated the effects of dezocine, a mu- and kappa-opioid receptor agonist/antagonist, on morphine tolerance and explored the involvement of opioid receptor expression in a rat model of bone cancer pain. METHODS: Thermal nociceptive thresholds were measured after the subcutaneous injection of morphine (10 mg/kg) alone or combined with dezocine (10 or 1 mg/kg) for 7 consecutive days. Real-time PCR and western blot analysis were used to examine opioid receptor expression in the periaqueductal gray (PAG) and spinal cord. RESULTS: The analgesic effect was significantly decreased after 4 days of morphine administration. We observed that low-dose dezocine significantly attenuated morphine tolerance without reducing the analgesic effect of morphine. Low-dose dezocine coadministration significantly reversed the downregulated expression of mu (MOR) and delta (DOR) opioid receptors in the PAG and the upregulated expression of kappa (KOR) and DOR in the spinal cord induced by morphine. Moreover, low-dose dezocine coadministered with morphine significantly inhibited KOR expression in both the PAG and spinal cord. CONCLUSIONS: The combination of low-dose dezocine with morphine may prevent or delay the development of morphine tolerance in a rat model of bone cancer pain. The regulation of opioid receptor expression in the PAG and spinal cord may be part of the mechanism.

Donepezil prevents morphine tolerance by regulating N-methyl-d-aspartate receptor, protein kinase C and CaM-dependent kinase II expression in rats.

Current studies have indicated that donepezil as a cholinesterase inhibitor can attenuate morphine-induced tolerance. The present study aimed to evaluate the possible role of N-methyl-d-aspartate receptors (NMDARs), protein kinase C (PKC) and CaM-dependent kinase II (CaMKII) pathways in this effect. Female Wistar rats received daily morphine (10 mg/kg, i.p.) alone or in combination with donepezil (1.5 or 2 mg/kg, gavaged) for 14 days. The analgesic effect was assessed by Von-frey, hotplate and tail flick test. On the 15th day, the periaqueductal gray (PAG) and lumbar spinal cord of rats were dissected. Then, protein levels of NMDAR-NR1, NR2B, PKCγ and CaMKIIα were tested using Western blot method. The results showed that morphine tolerance was seen after 8-10 days of injection compared with control group, while daily co-administration of donepezil with morphine prolonged the occurrence of analgesic tolerance. Western blot showed that morphine significantly increased NR1, PKCγ and CaMKIIα expressions in PAG, and significantly increased PKCγ and CaMKIIα in spinal cord. In contrast, donepezil downregulated NR1 and PKCγ in PAG, and downregulated PKCγ and CaMKIIα in spinal cord. Moreover, donepezil alone activates NR1 and NR2B in spinal cord, which needs to be further studied. Thus, the present results suggest that the attenuation effects of donepezil on morphine tolerance are possibly mediated by preventing morphine-induced upregulations in NR1, PKCγ and CaMKIIα expressions.

Genetic Variant of MYLK4 Gene and its Association with Growth Traits in Chinese Cattle.

As a member of MYLK family, MYLK4 gene may play a vital role in muscle development. In this study, one novel single-nucleotide polymorphism (SNP) was identified the bovine MYLK4 by sequencing pooled DNA samples (pool-Seq) and forced polymerase chain reaction-restriction fragment length polymorphism (forced PCR-RFLP) methods. Overall, we reported one mutation (SNP1) in the intron 10 region within the bovine MYLK4 gene in 559 individuals representing five main cattle breeds from China (Nanyang, NY; Qinchuan; Jiaxian, JX; Pinan cattle; and Caidamu cattle, CDM). Genotype AA and allele A were predominant in the QC, PN, and XN populations. Association analysis with growth traits in the QC breed showed that the animals with genotype GG had significantly greater chest breadth and hip width (P < 0.05). Meanwhile, the genotype GG was strongly associated with withers height and body length than those with genotype AA (P < 0.01 or P < 0.05) at 12 months in the NY breed. These statistical results exhibited that the MYLK4 gene might be a potential candidate gene to improve cattle's growth traits, and the SNP could be used as molecular markers in early marker-assisted selection (MAS) in beef cattle breeding program.

Low Concentration of Dezocine in Combination With Morphine Enhance the Postoperative Analgesia for Thoracotomy.

OBJECTIVE: When morphine and dezocine are mixed together, the clinical interactions with analgesic effects and adverse events remain unknown. The authors aimed to investigate the efficacy of low concentrations of dezocine in combination with morphine for postoperative pain. DESIGN: A prospective, randomized, double-blinded clinical trial. SETTING: Cancer Institute and Hospital, National Cancer Center, China. PARTICIPANTS: Sixty patients undergoing thoracotomy were randomized into 3 groups to investigate the analgesic efficacy of different ratios of morphine and dezocine. INTERVENTIONS: The morphine group (Group M) received morphine (1 mg/mL) alone for patient-controlled analgesia (PCA); the morphine+dezocine 1 group (Group MD1) received morphine (1 mg/mL) combined with dezocine (0.05 mg/mL) at a ratio of 20:1 for PCA; the morphine+dezocine 2 group (Group MD2) received morphine (1 mg/mL) combined with dezocine (0.1 mg/mL) at a ratio of 10:1 for PCA. Cumulative morphine consumption, verbal rating scores (VRS), and adverse events were evaluated throughout a 48-hour postoperative period. MEASUREMENTS AND MAIN RESULTS: Cumulative morphine requirements were (1) statistically higher in Group M than in Group MD2 at 24 and 48 hours after surgery and (2) statistically higher in Group M than Group MD1 at 48 hours after surgery. Postoperative VRS for evaluating pain were similar among the 3 groups. The incidence of postoperative nausea and pruritus was statistically higher in Group M than in Groups MD1 and MD2. The incidence of dizziness was not significantly different among groups. CONCLUSIONS: The combination of morphine and dezocine at the concentrations [morphine (mg/mL)]/[dezocine (mg/mL)] of 1/0.05 (ratio 20:1) and 1/0.1 (ratio 10:1) may enhance postoperative analgesia after thoracotomy.

Switching from morphine to fentanyl attenuates the decline of µ-opioid receptor expression in periaqueductal gray of rats with morphine tolerance.

BACKGROUND: Opioid switching is a therapeutic maneuver to improve analgesic response and/or reduce adverse side effects although the underlying mechanisms remain unknown. The µ-opioid receptor (MOR) has an important role in mediating the actions of morphine and other analgesic agents. This study is aimed at exploring the changes of MOR in the periaqueductal gray (PAG) in rats when morphine is substituted for equianalgesic fentanyl. METHODS: Forty rats were randomly assigned to five treatment groups: 7 days normal saline group (N group), 7 days fentanyl group (F group), 7 days morphine group (M group), 7 days morphine and 7 days fentanyl-switching group (MF group), and 14 days morphine group (MM group). Rats repeatedly received subcutaneous injections of morphine sulfate (10 mg/kg) or equianalgesic fentanyl sulfate (0.1 mg/kg) twice daily. Rats' antinociceptive response to thermal pain was evaluated by the tail flick latency assay. MOR mRNA and protein expression in the PAG were measured using RT-PCR and Western blotting analyses respectively. RESULTS: This study showed that after morphine was substituted with fentanyl on day 8, the tail flick latency (TFL) increased from (3.9 ± 0.4) seconds to (11.4 ± 0.4) seconds. The results also demonstrated that both MOR mRNA and protein expression in the PAG of rats in the MF group were less than that in the M group (P < 0.05) but more than that in MM group (P < 0.05). CONCLUSIONS: Equianalgesic fentanyl was still antinociceptive effective in rats with morphine tolerance, which may be due to the switching from morphine to fentanyl attenuating the decline of MOR expression in the PAG of rats.