CORE AND PENUMBRAL NITRIC OXIDE SYNTHASE ACTIVITY DURING FOCAL CEREBRAL ISCHEMIA AND REPERFUSION IN RATS

Abstract

S340 Introduction: Although the neurotoxic effects of nitric oxide during cerebral ischemia are recognized, [1] a differential effect of the severity of ischemia on cerebral nitric oxide synthase (NOS) activity has not been described. We measured NOS activity in ischemic core and penumbral brain areas after middle cerebral artery occlusion (MCAo) and reperfusion in rats. Methods: The protocol was approved by the animal care committee. Physiologic parameters were maintained within normal limits (cranial temperature-37[degree sign]C). During isoflurane anesthesia, MCAo was achieved by advancing a suture into the middle cerebral artery for 90-min. NOS activity (14) C-arginine[right arrow]14 C-citrulline) was measured in core and penumbral brain regions [2] in the ischemic hemisphere, and corresponding areas in the nonischemic hemisphere for three groups, before and after addition of NOS cofactors (tetrahydrobiopterin, flavin adenine dinucleotide, flavin mononucleotide): Controls (n=10)-after immediate decapitation (no MCAo); MCAo (n=11)-90-min of MCAo and no reperfusion; MCAo/R (n=9)-90-min of MCAo and 30-min of reperfusion. The data were evaluated by ANOVA. Results: Addition of cofactors increased NOS activity in all areas for all groups versus the corresponding area without cofactors. In all groups, core NOS activity was greater than penumbral NOS activity (p<0.05). In the ischemic core, NOS activity was less in the MCAo/R group than the MCAo group. Moreover, NOS activity in the core was significantly less than corresponding tissue from the right hemisphere (see Table 1).Table 1: NOS activity, without and with cofactors for the ischemic core (I-Core) and penumbral (I-Pen) areas, and for corresponding areas in the non-ischemic hemisphere (N-Core, N-Pen). The units are fmol[center dot]mg of prot-1[center dot]min-1 (mean +/- SEM). *p<0.05 versus the corresponding penumbral area. sup [dagger] p<0.05 versus the non-ischemic core. sup [double dagger] p<0.05 versus the MCAo group. sup & p<0.05 versus the corresponding area without cofactors.Discussion: The data demonstrate higher core than penumbral NOS activity before MCAo, during occlusion, and during early reperfusion. These differences suggest that NOS activity may act to define vulnerable areas of the brain to ischemia.