Regional blood flow in canine brain during nicotine infusion: pentobarbital vs. chloralose anesthesia.

We compared vasoactive effects of intravenous nicotine (36 micrograms/kg/min) in regional cerebral circulations under pentobarbital and chloralose anesthesia. Experiments were conducted in three groups of dogs: Group I, pentobarbital anesthesia with fixed ventilation; Group II, chloralose anesthesia with fixed ventilation; Group III, chloralose anesthesia with free breathing. Values for regional cerebral blood flow measured with 15 mu radioactive microspheres were used to compute regional cerebral vascular resistance (rCBR). In Group I, nicotine had no effect on rCVR in cerebral cortex, and it increased significantly rCVR in cerebellum (+17%), pons (+13%), medulla (+23%), and spinal cord (+19%). Using chloralose instead of pentobarbital in dogs with fixed ventilation (Group II), caused a significant reduction in rCVR in the cerebral cortex during nicotine, although it did not alter significantly nicotine-induced changes in rCVR in other regions of the brain. Hypocapnic alkalosis during nicotine-induced hyperventilation (Group III) resulted in significant increases in rCVR in all regions of the brain; however, the increases in rCVR in non-cortical regions more than doubled those in the cerebral cortex. The present results indicate: Nicotine-induced vasodilation in cerebral cortex was blunted by pentobarbital anesthesia. Nicotine-induced vasodilation in cerebral cortex under chloralose anesthesia was sufficient to nullify in part the potent vasoconstrictor effect of hypocapnic alkalosis.