LOCAL CEREBRAL BLOOD-FLOW AND GLUCOSE-UTILIZATION AFTER BLOOD-EXCHANGE WITH A HEMOGLOBIN-BASED O-2 CARRIER IN CONSCIOUS RATS

The effects of a blood exchange on cerebral blood flow and glucose uti lization were studied. A near to total blood exchange (hematocrit < 3% ) was achieved in conscious rats by isovolemic hemodilution. Ultra-pur ified, polymerized, bovine hemoglobin (UPBHB) served as a blood substi tute. Local cerebral blood flow (LCBF) and local cerebral glucose util ization (LCGU) were measured in 34 brain structures of conscious rats by means of the iodo[C-14]antipyrine and the 2-[C-14]-deoxy-D-glucose methods. A group of rats without blood exchange served as control. Aft er blood exchange LCBF increased from 36 to 126% in the different brai n structures resulting in a nearly doubled mean cerebral blood flow (82%). LCGU increased only moderately by 0-24%. Significant increases i n LCGU were observed in 16 brain structures. Mean cerebral glucose uti lization slightly increased (+14%). The relationship between LCGU and LCBF was found to be tight both in the control group (r = 0.95) as wel l as after blood replacement (r = 0.94), although it was reset to a hi gher overall LCBF-to-LCGU ratio. The profound increases in LCBF observ ed after blood exchange, which were not paralleled by comparable incre ases in LCGU, might be explained by a reduction of blood viscosity aft er blood exchange. Additional effects of blood exchange observed in th e present study were an increase of mean arterial blood pressure and a decline of heart rate. The results indicate that replacement of blood with the hemoglobin-based oxygen carrier UPBHB appears to meet the ce rebral circulatory and metabolic demands of the brain tissue.