Differential and non-uniform tissue and brain distribution of two distinctC-14-hexachlorobiphenyls in weanling rats

Excretion and tissue retention of a coplanar and a non-coplanar hexachlorob iphenyl (HxCB) were determined 48 h after a single intraperitoneal (ip) dos e of 8 mg/kg radiolabeled [C-14]-HxCBs to weanling male and female Long-Eva ns rats. The objective was to understand the involvement of initial target organs of chlorobiphenyl (CB) accumulation following acute exposure in imma ture animals. During the short interval, both HxCBs remained sequestered pr edominantly in mesenteric fat (compared to subcutaneous fat) and less than 1% of the doses were excreted. Excretion was 4- to 8-fold lower than adult rats. Coplanar CB 169 (3,3', 4,4', 5,5'-HxCB) did not accumulate appreciabl y in the brain, but was retained at 3-fold higher levels in the liver than was non-coplanar CB 153 (2,2', 4,4', 5,5'-HxCB). Accumulation of C-14-CB 15 3 in brains was 4- to 9-fold higher than that of C-14-CB 169 and was adequa te to detect non-uniform distribution in serial cryostat sections by phosph or imaging autoradiography. The autoradiographs showed a higher CB 153-deri ved radioactivity associated with fiber tracts throughout the brain. Specif ically, the corpus callosum, internal and external capsules, medial lemnisc us, tegmentum of the mesencephalon and metencephalon, and cerebellar pedunc les showed significantly higher C-14-CB 153 than the other structures. The 14C-CB 153 was not found in the ventricular system and vascular spaces. The se results suggest for the first time that an ortho-substituted PCB congene r accumulated preferentially in brain in a structure-specific manner when c ompared to a non-ortho-substituted PCB congener.