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.