nitroarginine and Spinal-Cord-Injuries

To determine whether reactive nitrogen species contribute to secondary damage in CNS injury, the time courses of nitric oxide, peroxynitrite, and nitrotyrosine production were measured following impact injury to the rat spinal cord. The concentration of nitric oxide measured by a nitric oxide-selective electrode dramatically increased immediately following injury and then quickly declined. Nitro-L-arginine reduced nitric oxide production. The extracellular concentration of peroxynitrite, measured by perfusing tyrosine through a microdialysis fiber into the cord and quantifying nitrotyrosine in the microdialysates, significantly increased after injury to 3.5 times the basal level, and superoxide dismutase and nitro-L-arginine completely blocked peroxynitrite production. Tyrosine nitration examined immunohistochemically significantly increased at 12 and 24 h postinjury, but not in sham-control sections. Mn(III) tetrakis(4-benzoic acid)-porphyrin (a novel cell-permeable superoxide dismutase mimetic) and nitro-L-arginine significantly reduced the numbers of nitrotyrosine-positive cells. Protein-bound nitrotyrosine was significantly higher in the injured tissue than in the sham-operated controls. These results demonstrate that traumatic injury increases nitric oxide and peroxynitrite production, thereby nitrating tyrosine, including protein-bound tyrosine. Together with our previous report that trauma increases superoxide, our results suggest that reactive nitrogen species cause secondary damage by nitrating protein through the pathway superoxide + nitric oxide peroxynitrite protein nitration.

Topics: Amino Acids; Animals; Immunohistochemistry; Male; Models, Biological; Nitrates; Nitric Oxide; Nitroarginine; Proteins; Rats; Rats, Sprague-Dawley; Spinal Cord; Spinal Cord Injuries; Superoxide Dismutase; Tyrosine; Wounds, Nonpenetrating

The extent to which nitric oxide (NO) is involved in the modulation of spinal cord blood flow (SCBF) in the uninjured and injured cord is unknown. To elucidate these questions, the following experiments in anesthetized rats were conducted.. Because NO is an unstable free radical with a half-life of seconds, its role can be understood through the study of the NO synthase inhibitor L-NG-nitroarginine (L-NOARG). L-NOARG was administered intravenously for 30 minutes at a dose of 100 or 500 micrograms/kg/min in 12 and 10 uninjured animals, respectively. SCBF fluctuations at C7-T1 were measured using laser doppler flowmetry. In a second set of 12 rats, L-NOARG (500 micrograms/kg/min) was administered 10 minutes before spinal cord injury using a modified aneurysm clip at C7-T1 and continued for 30 minutes thereafter.. In the uninjured animals, L-NOARG was associated with a dose-dependent increase in mean arterial pressure of 20 to 80% above baseline (P = 0.0001), together with a dose-related decrease in SCBF (P = 0.0373). In the injured animals, L-NOARG was associated with a 48% increase in mean arterial pressure. With L-NOARG, the changes in SCBF from baseline after injury were similar to those of noninjured controls (n = 25) and significantly less than injury controls (n = 18) or those receiving phenylephrine (n = 8).. NO synthase inhibitors, by reducing available NO, cause systemic vasoconstriction and a decrease in SCBF in the uninjured spinal cord. In the injured spinal cord, the administration of L-NOARG results in a redistribution of blood flow with an augmentation in posttraumatic SCBF at the injury site.

Topics: Animals; Blood Flow Velocity; Blood Pressure; Dose-Response Relationship, Drug; Infusions, Intravenous; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Rats; Rats, Wistar; Spinal Cord; Spinal Cord Injuries

Our previous studies have shown that nitric oxide synthase (NOS) can be induced in motoneurons after spinal root avulsion lesion and the lesion-induced NOS is coincident with the death of the injured neurons. The present study examined whether the death of injured motoneurons can be prevented by inhibition of NOS. Nitroarginine, a specific inhibitor of NOS, was injected into adult rats which underwent spinal root avulsion. At a dose of 50 mg/kg/day, nitroarginine significantly inhibited the activity of lesion-induced NOS and significantly reduced the death of motoneurons due to spinal root avulsion. Results of the present study indicate that NO, produced by lesion-induced NOS, may be involved in and responsible for the neuronal death after traumatic injury.

Topics: Amino Acid Oxidoreductases; Animals; Arginine; Cell Death; Histocytochemistry; Motor Neurons; Nitric Oxide Synthase; Nitroarginine; Rats; Rats, Sprague-Dawley; Spinal Cord Injuries