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INHIBITION OF NITRIC OXIDE SYNTHASE AFFECTS CEREBRAL CORTICAL BLOOD FLOW DURING HYPERTENSION IN NEWBORN PIGLETS. † 1157

Nitric oxide (NO) has a major role in the regulation of cerebral blood flow, however, its role in the autoregulation of cerebral blood flow remains unclear. These experiments examined the effect of inhibition of NO synthase by Nω-nitro-L-arginine methyl ester (L-NAME, 50 mg/kg) on total brain and regional blood flows (ml/min/100g) in 8 piglets (<14 d) at baseline and at an elevated MAP (110-125 mmHg) which is beyond the reported upper limit of autoregulation in newborn piglets. Blood flow was measured by radiolabelled microspheres. Piglets were anesthetized with α-chloralose and urethane. Catheters were placed in the left ventricle for microsphere injection, descending aorta, subclavian artery and dorsal sagittal sinus. MAP was increased by aortic occlusion and/or norepinephrine infusion. Cerebral perfusion pressure was elevated from baseline to 109 ± 1 mmHg in the control group and to 105 ± 3 in the L-NAME group. Cerebral cortical grey matter blood flow increased significantly (71 ± 6 to 129 ± 21) in controls (n=5) but not in L-NAME (69 ± 15 to 51 ± 1). Cortical flows were significantly different (p<0.01) among groups at the elevated pressure. Total brain blood flows tended to increase in controls (56± 10 to 71 ± 13) but not in L-NAME (59 ± 12 to 43± 1). Brain stem blood flows did not change significantly at these pressures. Cerebral oxygen consumption was not significantly affected by treatment with L-NAME or increased MAP. These results indicate that the non-selective inhibition of nitric oxide synthase significantly affects cerebral cortical blood flow in newborn piglets when MAP is elevated and suggest that NO production may play a regionally-specific role in the regulation of cerebral blood flow when cerebral perfusion pressure is increased.