The Effects of NG-Nitro-L-Arginine-Methyl Ester on Neurologic and Histopathologic Outcome After Transient Spinal Cord Ischemia in Rabbits

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Abstract
Little is known about the role of nitric oxide in the pathophysiology of spinal cord ischemia. We evaluated the effects of nitric oxide synthase (NOS) inhibition by NG-nitro-L-arginine-methyl ester (L-NAME) in rabbits whose abdominal aorta was occluded for 20 min (Experiment 1) or 25 min (Experiment 2). In Experiment 1, the L-NAME group (n = 6) received 3 mg/kg IV L-NAME, followed by an IV infusion of 3 mg · kg−1 · h−1 until 6 h after reperfusion. Ischemia was induced 20 min after the start of L-NAME. The phenylephrine group (n = 6) received phenylephrine to maintain comparable blood pressure. The control group (n = 6) received saline. In Experiment 2, L-NAME (3 mg/kg IV L-NAME, followed by an IV infusion of 3 mg · kg−1 · h−1 until 6 h after reperfusion) and phenylephrine groups (n = 6 each) were studied. Ischemia was induced 100 min after the start of L-NAME. Forty-eight hours after reperfusion, hindlimb motor function and histopathology of the spinal cord were examined. In Experiment 1, L-NAME and phenylephrine both improved neurologic outcome, with higher intraischemic blood pressures than saline. In Experiment 2, L-NAME worsened the neurologic and histopathologic outcome compared with phenylephrine. Attenuation of damage by L-NAME in Experiment 1 may be attributable to an intraischemic blood pressure increase. The worse outcome with L-NAME in Experiment 2 suggests that NOS inhibition exacerbates ischemic spinal cord damage. Implications Nonselective inhibition of nitric oxide synthase activity has aggravating effects on the neurologic and histopathologic outcome after transient spinal cord ischemia.