FIRST EVALUATION OF TC-99M DIMERCAPTOPROPIONYL ALBUMIN AS A POSSIBLE TRACER AGENT FOR VENTRICULOGRAPHY IN A VOLUNTEER

Technetium-99m labelled red blood cells (Tc-99m-RBCs) are the standard radiopharmaceutical for radionuclide ventriculography but suffer from some practical disadvantages such as risk of viral contamination and lengthy preparation (in vitro labelling) or poor labelling efficiency due to patient medication interactions (in vivo labelling). Tc-99m-lab elled human serum albumin (HSA) is not really a valuable alternative a s the activity diffuses too rapidly out of the vascular space due to t he weak binding of the radionuclide. We have modified HSA by reaction with N-hydroxysuccinimidyl 2,3-di(S-acetylmercapto)propionate (SAMP) t o introduce a varying number of 2,3-dimercaptopropionyl (DMP) side cha ins. The resulting DMP-HSA can be rapidly labelled with Tc-99m at room temperature by simple addition of stannous ions and eluate of a Tc-99 m generator. After evaluation in mice and rabbits, two different Tc-99 m-DMP-HSA preparations - obtained after reaction of SAMP with albumin in a molar ratio of, respectively, 8:1 and 16:1 - were tested in a vol unteer and compared to (99m)TCRBCs. The blood time-activity curves of the three preparations were quite similar but both Tc-99m-DMP-HSA prep arations were excreted much less into the urine than Tc-99m-RBCs. Vent riculography was performed with the three tracer agents, each time wit h a 1-week interval. In the three studies, the heart was clearly visua lized and the left and right ventricle could be easily delineated. The ejection fractions obtained after administration of the three prepara tions were similar. With both Tc-99m-DMP-HSA preparations the low acti vity in the spleen was a distinct advantage and facilitated delineatio n of the left ventricle. However, a slightly higher liver uptake was s een with Tc-99m-DMP-HSA 16:1, whereas the liver uptake of Tc-99m-DMP-H SA 8 :1 and Tc-99m-RBCs was the same. These first results suggest that Tc-99m-DMP-HSA, and in particular Tc-99m-DMP-HSA 8:1, could be used f or ventriculography as a practical and reliable alternative to Tc-99m- RBCs.