The regional changes of the catalytic NOS activity in the spinal cord of the rabbit after repeated sublethal ischemia

The regional distribution of catalytic NOS activity was studied in the lumb osacral segments of the spinal cord of the rabbit during single (8-min), tw ice (8-, 8-min) and thrice repeated (8-, 8-, 9-min) sublethal ischemia foll owed each time by lh of reperfusion. Single ischemia/reperfusion induced a significant increase of cNOS activity in almost all spinal cord regions, wi th the exception of non-significant increase in the dorsal horn. Sublethal ischemia repeated twice produced a significant decrease of enzyme activity in the intermediate zone and ventral horn and an increase in the white matt er columns. Within thrice repeated ischemia, the activity of cNOS in the gr ay matter regions was similar to that found after a single ischemia/reperfu sion. For all the animals subjected to single and twice repeated sublethal ischemic insults, there was no neurological impairment. Following thrice re peated ischemic insults, four out of five of the experimental animals recov ered only partially and one was completely paraplegic. Our results do not i ndicate a cumulative effect of repeated sublethal ischemia on cNOS activity and, consequently, on NO production. The NO generated during thrice repeat ed ischemia/reperfusion appears to have a detrimental effect on the neurolo gical outcome.