The effects of fentanyl and morphine on local blood flow and oxygen tension in the frontoparietal cortex and nucleus accumbens of the brain in white rats.

Studies on white rats showed that intraperitoneal administration of small doses of fentanyl (0.005 mg/kg) and morphine (1 mg/kg) decreased local blood flow and increased partial pressure of oxygen (pO2) in the frontoparietal area of the cerebral cortex but had the opposite effects in the nucleus accumbens--where there was a significant increase in local blood flow and just as significant a decrease in pO2. Analysis of the data led to the conclusion that these changes must result from significant changes in functional-metabolic activity in these structures, induced by intraperitoneal administration of fentanyl or morphine.