Decreased cerebrospinal fluid production by intravenous sodium diatrizoate

Intravenous administration of the radiographic contrast agent sodium diatrizoate (50%, 2ml/kg) significantly decreased cerebrospinal fluid (CSF) production in dogs for up to 40 minutes as measured from a lateral ventricular cannula. The magnitude of this decrease exceeded the decrease induced by hypertonic saline. Since hypertonicity could not explain the decrease, an enzymatic mechanism was sought. Choroid plexus carbonic anhydrase (CA) has been implicated in the elaboration of CSF. The assay of CA activity was a colorimetric measure of the hydration of CO2 where reaction time is related to the amount of active CA present. The inhibition of dog red blood cell and choroid plexus CA by sodium diatrizoate was compared with that by the known CA inhibitor acetazolamide. Acetazolamide (48 mM) produced almost complete inhibition whereas the inhibition by sodium diatrizoate (84 mM) was not significantly different from control. These results suggest that neither hypertonicity nor CA inhibition is the cause of the reduced CSF production after intravenous injection of sodium diatrizoate in dogs.