INTRATHECAL ADMINISTRATION OF N~ω-NITRO-L-ARGININE-METHYL-ESTER REDUCING THE NOCICEPTIVE HEAT RESPONSE IN RATS

Objective: To observe the effects of intrathecal administration of Nω-nitro-L-arginine-methyl-ester(L-NAME),a non-selective nitric oxide synthase inhibitor,on the nociceptive response to heat stimulus in the rats. Methods: Fifty female rats were randomly divided equally into five groups:Group A as control group,received intrathecal administration of normal saline 10 μg;Groups B,C,D and E as treatment groups,received intrathecal administration of L-NAME 2.5 μg, 25 μg, 250 μg and 2500 μg,respectively. As heat pain threshold, hindpaw withdrawal latency(HWL)was measured with hot plate before and every 5 min after intrathecal injection for 60 min. The algesic index(AI)was also calculated. Results:As compared to intrathecal administration of normal saline,intrathecal administration of L-NAME dose-dependently reduced the nociceptive response to heat in the rats. Conclusions: Nitric oxide plays an important role in spinal cord mechanism of hyperalgesia.