Calcium Antagonistic Effects of an Angiographic Contrasi Medium In Vitro

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Abstract
Vasodilatation is a well-known side effect of contrast media. Contrast media inhibit the action of vasoconstrictors. The nonionic contrast medium, iohexol, inhibits vasoactive substances to a lesser extent than ionic contrast media. Iohexol inhibited the action of vasoconstrictors in a way that raised suspicion of a calcium antagonistic effect of the medium. The authors test this hypothesis by comparing the inhibitory effect of iohexol with the inhibitory effect of a calcium antagonist (nifedipine). The vasoconstrictors were KCl, which depends on potential-operated calcium channels, and histamine, endothelin-1, and prostaglandin F2 alpha (PGF2 alpha), which depend on receptor-operated calcium channels. Segments of rabbit coronary arteries were mounted between two L-shaped prongs in tissue baths containing calcium-free buffer, calcium-free buffer with 10(-8) M nifedipine, or iohexol. One of the vasoconstrictors, KCl, histamine, endothelin-1, or PGF2 alpha, was added to induce a level of activation. Thereafter, increasing concentrations of CaCl2 were added in a stepwise manner, and the contractile responses of the vessel segments were recorded. Addition of CaCl2 caused concentration-dependent vasoconstrictions in the buffer. The effect of adding CaCl2 was inhibited in the buffer with nifedipine and in iohexol when the vessels were activated with histamine, endothelin-1, or PGF2 alpha. When the vessels were activated with the potential-operated calcium channel-dependent vasoconstrictor, KCl, the effect of adding CaCl2 was inhibited in the buffer with nifedipine but not in iohexol. In vitro, iohexol had the same effect as the calcium antagonist nifedipine on the action of receptor-operated calcium channel-dependent vasoconstrictors. This suggests a calcium antagonistic effect of iohexol on the action of the ROC.

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