DETERMINATION, STABLE-ISOTOPE ENRICHMENT AND KINETICS OF DIRECT-REACTING COPPER IN BLOOD-PLASMA

Direct-reacting Cu is defined as Cu2+ and other forms of Cu that readi ly exchange with Cu2+ in blood plasma. An analytical method was develo ped for 1) quantification of direct-reacting Cu by stable isotope dilu tion and 2) determination of Cu-65 enrichment of direct-reacting Cu in plasma samples from in vivo tracer studies. The method involved addit ion of enriched Cu-65 to plasma, extraction with sodium diethyldithioc arbamate in mineral oil, and analysis by inductively coupled plasma ma ss spectrometry. Optimum sodium diethyldithiocarbamate concentration f or the extraction was 0.16 mM. Direct-reacting Cu (means +/- SD) varie d from 3.4 +/- 0.5% of whole plasma Cu in dairy cows (n = 7) and 3.4 /- 0.3% in healthy men (n = 10) to 16.6 +/- 3.7% in dogs (n = 3). Afte r intravenous infusion of enriched Cu-65 into two healthy men, biologi cal half-lives of 8.7 and 12.3 min were determined for direct-reacting Cu.