Role of calcium in morphine dependence and naloxone-precipitated withdrawal in mice.

PURPOSE To explore the role of calcium in morphine withdrawal syndrome using various agents affecting calcium levels in cytoplasm. METHODS Mice were rendered dependent on morphine by subcutaneous injection of morphine, and withdrawal was induced 4 hours later by injecting the opioid antagonist, naloxone. Mice were observed for 30 minutes for signs of withdrawal, ie, characteristic jumping, hyperactivity, urination, and diarrhea. Various calcium channel blockers were injected intraperitoneally 30 minutes before naloxone to evaluate their influence on the severity of the withdrawal syndrome. We also tested the effect of combination levodopa-carbidopa pretreatment and its interaction with a selective alpha-1 blocker, terazosin, on naloxone-precipitated withdrawal in mice acutely dependent on morphine. RESULTS A significant dose-dependent attenuation of naloxone-induced morphine withdrawal syndrome was observed with calcium channel blockers, ie, verapamil 20 mg/kg (P < 0.05) and diltiazem 30 mg/kg (P < 0.01). Combination levodopa-carbidopa pretreatment facilitated the morphine withdrawal syndrome, and this was found to be blocked by terazosin, although not to a statistically significant (P > 0.05) extent. CONCLUSION The results indicate that calcium plays an important role in the genesis of morphine dependence and withdrawal, and suggest the usefulness of calcium channel blockers in the management of morphine withdrawal syndrome.