Increases in brain tumor and cerebral blood flow by blood-perfluorochemical emulsion (Fluosol-DA) exchange

It has been suggested that oxygen-carrying blood substitutes, perfluorochemical (PFC) emulsions, can increase blood flow and oxygen delivery to poorly perfused tumor regions. Local cerebral blood flow was measured in male Wistar rats bearing intracranial Walker 256 tumor with and without blood-PFC exchange using [14C]iodoantipyrine (IAP) and quantitative autoradiographic techniques. The exchange transfusion was performed in two groups of awake animals breathing 100% oxygen: (a) complete blood-PFC exchange, hematocrit 4%; and (b) partial blood-PFC exchange, hematocrit 20-25%. The tissue/blood partition coefficient for IAP was determined in a separate set of experiments under identical conditions and was used in calculating blood flow. Cerebral blood flow increased approximately 2-fold following complete blood-PFC exchange and 1.5-fold by the partial exchange. A similar 1.5-fold increase in flow was measured in intraparenchymal tumors following partial exchange; however, a flow increase was not identified in the meningeal extension of the tumors. The increase in cerebral blood flow is consistent with an autoregulatory response of the central nervous system vasculature to maintain an adequate supply of oxygen to central nervous system tissue. Presumably, the increase in blood flow to the intracerebral tumor reflects the autoregulatory response of the host tissue. The effect of blood-PFC exchange on blood flow and drug delivery to tumor may depend on the particular tumor and its site of growth (host tissue). The tissue/blood partition coefficient for IAP increased from 0.8 to 1.0 and 1.4 following partial and complete blood-PFC exchange, respectively. This change in the partition coefficient reflects the change in the intravascular fraction of IAP that is bound to plasma proteins. The enhanced therapeutic effect that has been reported in some experimental tumor models may result from a higher tissue/blood equilibrium distribution ratio (due to reduced plasma protein binding) resulting in a higher tissue exposure to certain drugs following PFC administration.