Effect of spinal infusion of L-NAME, a nitric oxide synthase inhibitor, on spinal tolerance and dependence induced by chronic intrathecal morphine in the rat.

Systemic L-NG-nitroarginine methyl ester or L-NAME (LN), a nitric oxide synthase inhibitor, has been reported to attenuate systemic opioid tolerance and withdrawal. Intrathecal co-administration of LN (100 and 500 nmol/microliter per h) with spinal morphine produced only a small diminishing attenuation of tolerance and attenuated only one of seven signs of withdrawal. These results show that LN has little effect on morphine tolerance and withdrawal at spinal sites.