Neural tissue uptake and clearance of iohexol following lumbar myelography in rabbits

The diffusion of water-soluble contrast media (CM) into the extracellular space of the central nervous system following injection into the subarachnoid space has previously been shown. As a result of this, water-soluble CM will come in direct contact with the neurons and may interfere with their normal function. The toxic effects would thus be a result both of the molecular properties of the CM as well as the local tissue concentration. The neuronal tissue uptake and clearance of metrizamide in rabbits following lumbar myelography was described in a previous study by our group. This study indicated some retention of metrizamide in the spinal cord probably as a result of binding of the CM to the cell membrane. The mechanism for this has not yet been shown although it may relate to the binding of metrizamide via its 2-deoxy-D-glucose (2-DG) portion and the specific glucose membrane carrier. The present investigation was performed to evaluate the diffusion kinetics of a new non-ionic CM. With iohexol, which lacks a 2-DG component in its molecule a direct relationship between the neural tissue and CSF concentration was found which seems to follow a simple diffusion model. Since iohexol shows no sign of entrapment in the tissue, the contact time for neurons will be shorter than that seen with metrizamide assuming that their rate of drainage from the CSF is identical.