GADOLINIUM(III) INVIVO SPECIATION .2. A POTENTIOMETRIC STUDY OF GADOLINIUM(III) AMINO-ACID COMPLEXES

Gadolinium(III) complexes of valine, alanine, glycine, threonine, and glutamine have been studied potentiometrically at 25-degrees-C and an ionic strength of 0,15 mol dm-3 NaCl. These results have been used in a computer model to calculate the gadolinium(III) species distribution in blood plasma. The results indicate that these amino acid complexes are not important in vivo, but that at low concentration (< 2 x 10(-4) mol dm-3) the metal ion is bound almost exclusively as [Gd(citrate)(OH)]- (69,1%) and [Gd(citrate)(OH)2]2- (24,4%). At higher concentrations the metal ion is distributed over several complexes with [Gd(lactate)]2+ (9,0%) becoming important. The inclusion of transferrin bound by Gd(III) in the simulation (uptake of Gd(III) by transferrin is slow) shows that at 2 x 10(-4 )mol dm-3 Gd(III) at most 36,9% of the Gd(III) will be bound to transferrin [Gd2(transferrin)].