Effects of free and liposome-encapsulated hemoglobin on choroidal vascular plexus blood flow, using the rabbit eye as a model system.

Abstract

This study investigated the vasoconstrictive effects of both stroma-free and liposome-encapsulated cross-linked hemoglobin (Hb) on vascular plexus hemodynamics, using the choroid of the rabbit eye as a model system. Sequential subtraction of high-speed ICG fluorescence angiogram images facilitated visualization of the time-varying patterns of blood flow distribution in the choriocapillaris during the cardiac cycle. Differences between baseline and post-hemoglobin injection blood flow distributions were analyzed. Likewise, differences in the time-varying patterns of flow distribution between the particulate and liquid phases of blood during a cardiac cycle were investigated, since this may bear on differences in vasoactivity induced by circulating stroma-free vs. encapsulated Hb. Cross-linked Hb induced a transient, but marked, localized reduction in choriocapillaris blood flow. This effect was significantly attenuated when liposome encapsulated cross-linked hemoglobin was administered. Plexus blood flow distribution was different for particulate and liquid ICG. Differences in particulate and liquid ICG flow patterns suggest that one contribution to the different plexus blood flow patterns observed in the encapsulated and free Hb experiments may be due to differences in liquid and particle-bound Hb distribution within the plexus. The observed choriocapillaris blood flow reductions may be attributable to an aggregate endothelial cell contractility induced by presence of extra-cellular Hb in the choriocapillaris plexus.