MEASUREMENT OF CHEMICALLY-INDUCED CELL-PROLIFERATION IN RODENT LIVER AND KIDNEY - A COMPARISON OF 5-BROMO-2'-DEOXYURIDINE AND [H-3] THYMIDINE ADMINISTERED BY INJECTION OR OSMOTIC PUMP

Different labeling methods for quantitating cell proliferation were evaluated in livers and kidneys of control and chemically treated mice and rats. The percentage of cells in S-phase (labeling indices) were compared in tissues of animals given either 5-bromo-2'-deoxyuridine (BRDU) or [H-3]thymidine. These DNA precursor labels were delivered either by a single i.p. injection 2 h prior to killing the animals or via the s.c. implanted osmotic pump for 3 or 6 days. B6C3F1 mice and male F344 rats were exposed to either a peroxisome proliferator and hepatocarcinogen, Wy-14,643 (WY), in the diet at 0.1% for up to 5 days, or a non-genotoxic mouse liver and male rat kidney carcinogen, 1,4-dichlorobenzene (DCB), in corn oil by gavage for up to 5 days in mice (600 mg/kg/day) or up to 3 weeks in rats (300 mg/kg/day, 5 days per week). Labeling indices (LIs) in the liver and kidney were similar in BRDU- and [H-3]thymidine-labeled mice and rats. Cell proliferation was increased in the livers of both species of WY- and DCB-treated animals when compared to controls. After 4 days of chemical treatment with continuous administration of a DNA precursor label during the last 3 days of treatment, LIs in controls, DCB- and WY-treated mouse livers were 0.7, 19 and 17% for BRDU and 0.9, 15 and 13% for [H-3]thymidine respectively. Furthermore, BRDU and [H-3]thymidine labeled the same population of cells as revealed by similar patterns of cell labeling in the livers and kidneys of treated animals. The LI for BRDU- and [H-3]thymidine-labeled renal proximal tubular cells was 7.7 and 8.0% respectively, in rats receiving DCB for 4 days and DNA precursor label during the last 3 days of treatment, while the LI for controls was 4.3 and 3.7% respectively. The renal proximal tubular cell LI increased to 11% in BRDU-labeled rats treated with DCB for 3 weeks. LIs in both liver and kidney were greatest in control and treated animals that received the DNA precursor label via osmotic pumps for 6 days, and least in 2 h pulse-labeled animals. However, induction of hepatic LI in treated over control animals was greatest for treated animals labeled for 3 days. These results demonstrate comparable cell labeling of cells in S-phase with either BRDU and [H-3]thymidine labeling methods. BRDU presents no radioactive containment problems, and results are obtained more rapidly than [H-3]thymidine. In the present study, BRDU administered in a 3 day osmotic pump was judged to be the method of choice for assessing chemically induced cell proliferation.