Distribution of TmDOTP5- in rat tissues: TmDOTP5- vs. CoEDTA- as markers of extracellular tissue space.
The distribution of TmDOTP5- in rat tissue was compared with CoEDTA-, an anionic complex previously used as a marker of extracellular space. Heart, liver, muscle, blood, and urine were collected from rats after infusion of either complex and were quantitatively analyzed by atomic absorption spectroscopy. Although total TmDOTP5- in blood and tissue was consistently lower (0.88 +/- 0.04; n = 6) than CoEDTA- after an identical infusion protocol (presumably because of some association of the phosphonate complex with bone), a comparison of blood and tissue contents indicated that the two anionic complexes distributed into identical extracellular spaces. Relative extracellular space in the in vivo liver, as determined by TmDOTP5- and CoEDTA-, was 0.18 +/- 0.02 and 0.15 +/- 0.01, respectively. The corresponding relative extracellular space values for the in vivo heart reported by the two agents were identical (0. 11 +/- 0.02). Experiments were also performed to evaluate the washout kinetics of TmDOTP5- from anesthesized rats. In rats given a total dose of 0.16 mmol TmDOTP5-, 81% appeared in urine by 180 min, <2% was found in all remaining soft tissue, leaving approximately 18% undetected. The rate of Tm appearance in urine was fit to a standard pharmacokinetic model that included four tissue compartments: plasma, one fast equilbrating space, one slow equilibrating space, and one very slow equilibrating space (presumably bone). The best fit result suggests that the highly charged TmDOTP5- complex is cleared from plasma more rapidly than is the typical lower charged Gd-based contrast agents and that release from bone is slow compared with renal clearance.
Makos
J D
JD
Department of Chemistry, University of Texas at Dallas, Richardson, 75083-0688, Texas, USA.
Malloy
C R
CR
Sherry
A D
AD
D000818:Animals; D002118:Calcium / Q000097:blood; D002614:Chelating Agents / Q000493:pharmacokinetics; D004492:Edetic Acid / Q000493:pharmacokinetics / Q000652:urine; D005110:Extracellular Space / Q000378:metabolism*; D008099:Liver / Q000378:metabolism; D008274:Magnesium / Q000097:blood; D008297:Male; D008954:Models, Biological; D009206:Myocardium / Q000378:metabolism; D009942:Organometallic Compounds / Q000493:pharmacokinetics / Q000652:urine; D009943:Organophosphorus Compounds / Q000493:pharmacokinetics / Q000652:urine; D051381:Rats; D017207:Rats, Sprague-Dawley; D013054:Spectrophotometry, Atomic; D013932:Thulium / Q000097:blood / Q000493:pharmacokinetics / Q000652:urine; D014018:Tissue Distribution
D002614:Chelating Agents; D009942:Organometallic Compounds; D009943:Organophosphorus Compounds; C069929:thulium(III) 1,4,7,10-tetraazacyclododecane-N,N',N'',N'''-tetramethylenephosphonate; D013932:Thulium; D004492:Edetic Acid; D008274:Magnesium; D002118:Calcium