Effects of vasoconstrictors on rabbit coronary arteries exposed to isotonic ionic and nonionic contrast media

Vasodilation is a well-known side effect of contrast media (CM) that is primarily explained by the hyperosmolality of the media. Few reports have dealt with the influences of chemotoxicity and ion toxicity on vessel tone. We compared the effects of solutions iso-osmolar to plasma of iohexol (nonionic monomer), ioxaglate (ionic dimer), diatrizoate (ionic monomer), and mannitol on responses to vasoconstrictors (potassium chloride [KCl], histamine, and endothelin-1). The aim of this study was to investigate if differences in chemotoxicity and ion toxicity could contribute to the changes in vessel tone seen clinically during arteriography.

Segments of rabbit coronary arteries were mounted between two L-shaped prongs in tissue baths with buffer solution or CM solutions. Their responses to increasing concentrations of a vasoconstrictor were measured. The maximal contraction of the vasoconstrictor (Emax) and the concentration of the vasoconstrictor causing half maximal contraction (EC50) were calculated.

Iohexol caused the same changes as the nonionic solution of mannitol. The media reduced the actions of KCl, histamine, and endothelin-1 to 50% to 60% of their action in buffer. The ionic CM, ioxaglate and diatrizoate, caused a more pronounced inhibition of histamine and almost totally inhibited the action of KCl. The action of endothelin-1 was inhibited to a greater extent by iohexol and mannitol than by ioxaglate and diatrizoate.

Different types of iso-osmolar CM interact differently with vasoconstrictors. These effects are caused by differences in chemo- and ion toxicity. These interactions might contribute to the differences in vasodilatation found clinically.