CSF cation changes following subarachnoid injection of iohexol and metrizamide in rabbits.

Forty anaesthetized rabbits were injected subarachnoidally with equimolal doses, 0.48 mmol/kg body weight (= 185 mg I/kg), of iohexol and metrizamide, administered in solutions iso- and hyperosmolal to the CSF. Concentrations of Na, K, Ca and Mg in the CSF were determined before and 3 hours after the contrast medium injections. Iso-osmolal iohexol caused a uniform decrease in all four cations, which was believed to be a simple dilution. The hyperosmolal solution of iohexol caused a significant relative increase in Ca compared with Na, K and Mg. Both metrizamide solutions caused an increase in Ca over its pre-injection level and a significant relative increase of both Ca and Mg as compared with Na and K. The changes caused by the three latter solutions were consistent with an increase in the blood-brain barrier permeability.