Action of gadolinium complexes on different enzyme systems.

Gadolinium complexes have two advantages: their toxicity is very low and the paramagnetic properties are adequate enough to give a useful signal with magnetic resonance imaging (MRI). The effects of several MRI contrast media on the activity of two brain enzymes, glutamate decarboxylase (GAD) and cholineacetyl transferase (ChAT), were investigated. The study was performed on homogenates of rat striatum with variable concentrations of gadolinium sulphate, EDTA, DTPA, DOTA, Gd-EDTA, Gd-DTPA and Gd-DOTA (from 10(-2) mol/l to 10(-9) mol/l. Gadolinium in its ionic form and the chelators of cation agents such as EDTA, DTPA and DOTA inhibit GAD, a calcium dependent enzyme, whereas they have no inhibiting effect on the activity of ChAT, a calcium independent enzyme. Gadolinium complexes inhibit the GAD activity by about 15 per cent whereas they do not modify that of ChAT. The complex form of gadolinium has the advantage of retaining its paramagnetism while drastically lowering its toxicity.