A simple new method for repeated in vivo cerebral cortex flux measurement in rats.

A new application of an indicator dilution technique, using nonradioactive para-aminohippuric acid, is described for superior sagittal sinus blood flow determination in rats. Superior sagittal sinus blood flow, mainly representing cerebral cortex blood flow, amounted to 541 +/- 49 microliters/min in ketamine-anesthetized, but otherwise normal, rats breathing room air. Increasing arterial pCO2 enhanced superior sagittal sinus blood flow (P less than 0.01), providing evidence that this method correctly measures cerebral blood flow. The respiratory quotient was 1.1 and the cerebral cortex metabolic rate of oxygen consumption was +/- 1.45 mumol/min. Cerebral cortex ammonia uptake was not significantly different from zero and of the amino acid fluxes, only alanine differed from zero (P less than 0.05). Flux measurements are crucial in studies of healthy or altered organ metabolism in both experimental animals and postoperative surgical patients. We devised a simple and economical method of repeated cerebral cortex flux measurement in rats that is a potentially valuable tool in metabolic studies of the cerebral cortex.