Effect of naltrexone on regional brain oxygen consumption in the cat

Cerebral blood flow was measured by 141Ce and 85Sr microsphere accumulation, and oxygen saturation of arterial and venous blood within 9 regions of the brain was determined by microspectrophotometric measurement in chloralose anesthetized cats. Extraction was calculated as the difference between oxygen content of arterial and venous blood. Oxygen consumption was computed as the product of blood flow and oxygen extraction. Global and regional comparisons were made between 7 anesthetized cats and 7 anesthetized cats given 1 mg/kg naltrexone HCl i.v. Naltrexone treatment reduced total brain oxygen consumption by 48% at 20 min after intravenous injection. Analysis of the anterior and posterior cortex, lenticulate nuclei, hippocampus, thalamus, hypothalamus, medulla, pons and cerebellum indicated that the oxygen consumption of the pons and hypothalamus was reduced to the greatest extent. The decreased oxygen consumption reduced blood flow in the whole brain, and the pons. The oxygen supply to consumption ratio was not altered by naltrexone except in the hypothalamus where an even greater excess of oxygen was delivered. These observations are interpreted as indicating that opiate receptor blockade is associated with reduced brain metabolism and that this response is not restricted to regions of high opiate receptor concentration.