Catecholamines and the relationship between cerebral blood flow and glucose use

The effects of hypertension induced by norepinephrine and dopamine infusion on the relationship between local cerebral blood flow (CBF) and local glucose use (GU) were examined in rats with the use of quantitative autoradiographic techniques. After rats recovered from anesthesia, dopamine or norepinephrine was infused at a rate that ensured moderate hypertension [mean arterial blood pressure (MABP) approximately 150 mmHg]. During dopamine infusion (approximately 200 micrograms X kg-1 X min-1), overall CBF-to-GU ratio throughout the brain was elevated (P less than 0.0001) when compared with saline controls. In contrast, during norepinephrine infusion (approximately 10 micrograms X kg-1 X min-1), the overall CBF-to-GU relationship was not altered significantly. The differential effect of the catecholamines was a consequence of the marked increases in local CBF and moderate decreases in GU observed during dopamine infusion, whereas during norepinephrine administration CBF and GU were not significantly altered in most brain regions. Blood-brain barrier (BBB) permeability was increased during moderate hypertension induced by dopamine and not when induced by norepinephrine. During extreme hypertension (MABP greater than 165 mmHg), heterogeneous increases in CBF and BBB permeability occurred (e.g., in the cerebellum and thalamus). Thus the cerebrovascular response to catecholamine infusion was critically dependent on the agent administered, the level of hypertension achieved, and the brain region examined.