Iohexol Inhibits Adenylate Cyclase

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Abstract
Previous studies demonstrated that the intravenous administration of the ionic radiographic contrast agent, diatrizoate, and the nonionic agent, iohexol, causes a decrease in the rate of cerebrospinal fluid (CSF) production. Evidence suggests that adrenergicmediated adenylate cyclase (AC) activity controls CSF production. Diatrizoate was found to inhibit AC activity. The authors now report that iohexol inhibits activity of this enzyme. Adenylate cyclase activity was measured in membrane fractions of bovine choroid plexus in the presence of various concentrations of iohexol. A concentration-dependent inhibition of basal and adrenergic-stimulated AC activity by the contrast agent was observed. The concentration of iohexol that produced a 50% inhibition was about 2.3 mM. This is similar to the concentration of diatrizoate that produced equivalent enzyme inhibition. These results support the contention that one mechanism for the action of contrast media in reducing CSF production involves inhibition of AC activity.