Effect of radiological iodinated contrast media on acetylcholinesterase activity

Abstract

The inhibitory effects of several contrast media on acetylcholinesterase (AchE) activity were studied in vitro. Their inhibiting power was in the order: iothalamate > ioxaglate > iopamidol > iohexol. Because both the Km and maximal velocity (V max) values of the enzyme were altered on adding ioxaglate, the inhibition mode seemed to be of a mixed type. Complete recovery from such inhibition was observed by removing the contrast media from the enzyme. Adding albumin (1%) to the reaction mixture led to a decrease in the inhibitory effect of ioxaglate. These results suggest that the contrast media, which have an inhibitory effect on AchE activity in vitro, may have no influence on its activity in blood which contains 4–5% of albumin under physiological conditions. Radiological iodinated contrast media are relatively non-toxic, but they are employed in such large doses that mild toxic effects are common in clinical practice, and severe reactions sometimes occur (Labbe & Peyroux, 1984; Dawson, 1983, 1985). Since some symptoms of their toxicity such as peripheral vasodilation, bronchospasm and disturbances of cardiac rhythm are similar to those produced by acetylcholine, their inhibitory effects on AchE (acetylcholine acetylhydrolase, EC 3117) have been studied (Lasser & Lang, 1966; Dawson & Edgerton, 1983; Howell & Dawson, 1985; Guidollet et al, 1988). The published studies, however, have yielded conflicting results. In this short communication, we report more precisely the nature of the inhibition of AchE by some representative ionic and non-ionic contrast media.