The Effects of Nitric Oxide on Oxygen Balance in Cerebral Ischemia

Lee, Doo Ik; Choi, Young Kyu; Chi, Oak Za

Abstract

Bockground: Nitric oxide (NO) is an important regulator of blood flow and also works as a neuronal messenger via cyclic GMP. Recent studies regarding the therapeutic utility of nitric oxide synthase (NOS) inhibitors in reducing ischemia-induced neuronal damage are very controversial. The possible neuroprotective effect of NO or NOS inhibitors in ischemic neuronal damage could occur at the vascular and or neuronal level. This study investigated whether the NOS inhibitor, NG-nitro-L-arginine-methyl ester (L-NAME) would alter oxygen balance in ischemic cerebrocortex of isoflurane-anesthetized rats.
METHODS
Fifteen minutes after middle cerebral artery occlusion, L-NAME (1.5 mgxmin-1kg-1) was infused intravenously to the L-NAME group (n=14), and normal saline was given to the control group (n=14) for 45 minutes. Regional cerebral blood flow was determined with [14C]iodoantipyrine, and arterial and venous oxygen saturations were determined by microspectrophotometry.
RESULTS
Regional cerebral blood flow of the ischemic cortex was significantly lower than that of the contralateral cortex in both groups. In the control group, ischemic cortex; 55+/-13, contralateral cortex; 110+/-29 mlxmin-1100 g-1, and in the L-NAME group, ischemic cortex; 35+/-13, contralateral cortex; 90+/-24 mlxmin-1100 g-1. Compared with the blood flow in the ischemic cortex of the control group, L-NAME significantly reduced ischemic blood flow by 36%. Venous oxygen saturation was significantly increased in the ischemic cortex (41+/-1% in control, 44+/-3% in L-NAME) but decreased in the contralateral cortex (65+/-3% in control, 61+/-3% in L-NAME) by L-NAME. Ischemic cortical oxygen consumption in the L-NAME group was 39% lower than that in the corresponding control group, whereas the difference was only 11% in the contralateral sides between groups. The ratio of oxygen supply to consumption was lower in the ischemic than in the nonischemic regions in both groups. In the ischemic cortex, this ratio was significantly lower in the control group (1.7+/-0.1) than in the L-NAME group (1.9+/-0.1). In contrast, the ratio tended to be decreased by L-NAME in nonischemic regions.
CONCLUSIONS
These observations suggest that despite a decrease in cerebral blood flow, inhibition of nitric oxide synthesis mildly improves the oxygen supply and consumption balance in the ischemic cortex.