Vasodilator and hemorheological effects of iodinated contrast media

Iodinated radiographic contrast media (IRCM) cause significant changes in blood flow following intraarterial and intravenous administration. These changes are predominantly due to alte rations in vascular tone, but are also influenced by contrast media viscosity and their effects on blood theology. The cellular mechanisms that underlie the changes in vascular tone still remain to be fully elucidated, but may include (i) effects attributable to hyperosmolality, (ii) protein binding and enzyme inhibition, (iii) stimulation of the release of endogenous vasoactive mediators and (iv) direct relaxant effects upon vascular smooth muscle. The influence of IRCM viscosity on blood flow, and of both viscosity and osmolality on blood rheology are also quite poorly understood. However, it is now apparent that at iodine concentrations which provide equivalent angiographic contrast, the hemorheological effects are significantly less with the newer hexaiodinated dimers, such as iodixanol and iotrolan, than with the older generations of compounds. The purpose of this review is to discuss the multifactorial effect of IRCM on the control of blood flow and to identify why the nonionic dimers represent a more hemodynamically inert alternative to conventional agents.