Comparative adipose tissue kinetics of thiopental, DDE and 2,4,5,2',4',5'-hexachlorobiphenyl in the rat

A comparative study on the fate of thiopental, DDE, and 2,4,5,2',4',5'-hexachlorobiphenyl (6-CB) with emphasis on adipose tissue kinetics was carried out after single i.v. doses to adult male rats. The time course of the concn. in blood, adipose and other tissues were determined for the three compounds for periods up to 40 h, 14 and 28 d, respectively, allowing for mass balances and for calculation of pharmacokinetic parameters. Appreciable amounts of thiopental, DDE and 6-CB appeared in adipose tissues, but the kinetics were profoundly different, the adipose tissue concn. peaking after one hour, 17 h, and five to six weeks, respectively. Thus, although DDE and 6-CB are much more lipophilic than thiopental, they were very much slower in entering adipose tissue. The results indicate that adipose tissue storage of drugs and other xenobiotics cannot be explained as a simple partition phenomenon. Rather, disposition in adipose tissue may be determined by initial binding in other tissues.