Anesthetics affect the cerebral metabolic response to circulatory catecholamines

This study examined whether the effect of intravenous infusions of either epinephrine or norepinephrine on cerebral metabolic rate for oxygen (CMRO2) in the dog was modified by different anesthetics. Infusions of either epinephrine or norepinephrine at rates of 0.1-0.25 mu.kg-1.min-1 reversibly increased the CMRO2 by 17-23% during anesthesia with cyclopropane 20% and nitrous oxide 50% in oxygen, whereas infusions at rates of 0.1-25.0 micrograms.kg-1.min-1 had no effect in dogs anesthetized with other inhalational or intravenous agents. Cyclopropane/nitrous oxide also increased permeability of the blood-brain barrier to Evan's blue dye whereas the other anesthetics tested did not. It is concluded that epinephrine and norepinephrine crossed the blood-brain barrier during cyclopropane anesthesia, accounting for the increase in CMRO2. The authors speculate that cyclopropane may have increased blood-brain barrier permeability by a direct effect on endothelial cells or by affecting central adrenergic systems and that epinephrine or norepinephrine may increase CMRO2 either by a direct action on neuronal receptors or via metabolically coupled synaptic events.