Purpose: In vivo fluorescence microscopy was used in experimental studies of renal cortical microcirculation in mice. The effects of i.v. infusion of a nonionic monomeric contrast medium (iohexol), a nonionic dimeric contrast medium (iodixanol), and mannitol of corresponding osmolalities were studied.
Results: All infusions produced marked effects on the distribution and velocity of renal cortical blood flow. Renal cortical blood flow was inhomogeneous as regards the different capillaries. There was an initial rapid rise in the blood flow in some capillaries after all infusions, while decreased flow was seen in other capillaries. The initial increase in renal cortical blood flow (RCBF) was significantly (p < 0.05) more pronounced after infusion of iohexol than after infusion of mannitol 0.69 mol/l. In all other respects, the effects of contrast media on RCBF were the same as the effects of mannitol solutions with a corresponding osmolality. The effects of each contrast medium were the same as those of mannitol of corresponding osmolality. In the capillaries showing increased blood flow, the peak value was encountered slightly later after the infusion of iodixanol than after the infusion of iohexol. This was considered to be related to differences in viscosity rather than osmolality.
Conclusion: The difference in osmolality between iodixanol and iohexol is of no significance with regard to their effects on RCBF.