Involvement of dynorphin A in the inhibition of morphine physical dependence by N-nitro-L-arginine in rats

Objective To investigate the involvement of immunoreactive dynorphin A in the inhibitory effect of N nitro L arginine on the morphine physical dependence in rats Methods The rats were rendered dependent on morphine by subcutaneous administration of morphine solution three times daily in a manner of dose increment of 5 mg·kg 1 for 6 days The degree of morphine physical dependence was monitored by scoring the abstinence syndromes precipitated by 5 mg·kg 1 naloxone of the rats The expression levels of immunoreactive dynorphin A in tissues were determined using a radioimmunoassay Results Intraperitoneal injection of 5 mg·kg 1 N nitro L arginine suppresses most of the withdrawal symptoms of morphine dependent rats N nitro L arginine can elevate the expression of immunoreactive dynorphin Conclusions Chronic N nitro L arginine administration can inhibit the development of morphine physical dependence in a manner of dose dependence, which is significantly related to its role of regulating the endogeneous dynorphin system