THE CORTICAL EPITHELIUM OF THE RAT THYMUS AFTER INVIVO EXPOSURE TO BIS(TRI-N-BUTYLTIN)OXIDE (TBTO) - AN (IMMUNO)HISTOLOGICAL AND ULTRASTRUCTURAL-STUDY

Bis(tri-n-butyltin)oxide (TBTO) induces cortical atrophy in the rat th ymus. We studied the potential involvement of the cortical epithelium in TBTO-induced thymotoxicity by (immuno) histology and electron micro scopy. Juvenile male Wistar rats were orally intubated once with eithe r 30 or 90 mg/kg TBTO and sacrificed 4 or 10 days later. A dose-depend ent thymic atrophy occurred. Anti-keratin labelling showed epithelial cell aggregation in some animals at 10 days after exposure to 90 mg/kg TBTO, when recovery of the thymus was apparent. At the ultrastructura l level, a relative shift was observed from ''pale'' to darker epithel ial cell subtypes at the 30 mg/kg dose level, both at day 4 and day 10 after intubation. This phenomenon was not observed after exposure to 90 mg/kg TBTO. Both the altered keratin distribution and the increased electron density of the epithelium probably represent non-specific ph enomena. The present morphological observations support the concept th at TBTO affects the thymus via its action on lymphoid cells rather tha n on the epithelial compartment.