ORGAN-SPECIFIC AND TRANSPLACENTAL DNA-DAMAGE AND ITS REPAIR IN RATS TREATED WITH 1,2-DIBROMO-3-CHLOROPROPANE

An in vivo genotoxicity assay system based on alkaline elution has bee n used to study the formation and removal of DNA damage induced by 1,2 -dibromo-3-chloropropane (DBCP). Cells/nuclei from different tissues a nd organs of Wistar rats were prepared by a rapid mincing/homogenizati on technique. Thirty-six samples of which up to 11 were from different organs of the same animal. were then assayed in parallel for DNA dama ge (DNA single-strand breaks plus alkali-labile sites = SSBs) with a s emi-automated alkaline elution system. A single i.p. injection of DBCP gave dose- (5 and 10 mg/kg) and time- (20 min-4 h) dependent SSBs in kidney and liver DNA from male rats. At 10 mg/kg DBCP, SSBs were forme d in all organs examined except the bone marrow and colon: however. an increased dose of 40 mg/kg produced SSBs also in the latter two organ s. The relative susceptibilities to DBCP-induced DNA damage were: kidn ey similar to duodenum > liver > lung similar to brain similar to urin ary bladder similar to glandular stomach > spleen similar to testis > bone marrow similar to colon. These relative levels correlate with pre vious data on tissue distribution and organ necrosis in liver. kidney and testis of rats given a single i.p. dose of DBCP. When female rats were injected i.p. with 5, 10 or 20 mg/kg (non-hepatotoxic doses) at d ay 20 of pregnancy. similar levels of SSBs were detected in the livers of the dam and the fetuses. In adult male rats, time-dependent change s in SSBs were followed in the liver and kidney after DBCP exposure. I n both organs SSBs peaked around 4 h post-exposure, 50%, had been remo ved by 12-24 h, whereas at day 2-3 SSB frequencies had returned to con trol levels. Pretreatment of rats with phenobarbital prior to DBCP exp osure reduced the maximum level of DNA damage as well as its persisten ce. In cultured primary hepatocytes from male rats exposed in vitro to DBCP (2-20 mu M, 1 h), 50% of the initial DNA damage had been repaire d within similar to 100 min. In conclusion, the experiments indicate t hat the distribution characteristics of DBCP are of major importance f or DNA damage and its persistence in various organs of rats. The data are also in accordance with glutathione-S-transferase, rather than P45 0, being the most important pathway for metabolic activation of DBCP i n rat extrahepatic tissues including the fetal liver. It appears that alkaline elution of cells/nuclei prepared from exposed animals constit utes a sensitive, rapid and versatile technique to study organ- and ce ll-specific genotoxicity in vivo.