Elevation of brain norepinephrine concentration after experimental subarachnoid hemorrhage

Regional brain tissue catecholamine concentrations were measured in 5 control rats and in 10 rats 72 hours after experimental subarachnoid hemorrhage (SAH). Catecholamine levels were determined in the cerebral hemispheres, brain stem, and cerebellum of each animal using a radioenzymatic assay. Three days after SAH, the tissue concentration of norepinephrine (NE) in the cerebral hemispheres was 64% greater than that in control rats (P < 0.001). NE levels did not change significantly in either the brain stem or the cerebellum. Most if not all of the NE in the brain tissue rostral to the brain stem is derived from neurons that originate in the locus coeruleus (LC). These data may therefore indicate that the LC is activated after SAH. The possible pathophysiological consequences of activation of the LC in relation to delayed cerebral ischemia after SAH will be discussed.