Transplacental mutagenicity of N-ethyl-N-nitrosourea at the hprt locus in T-lymphocytes of exposed B6C3F1 mice

Previous studies have compared age-related differences in total mutagenic b urden in mice of differing age (preweanling, weanling, or young adult) afte r single intraperitoneal (i.p.) injections of ethylnitrosourea (ENU). The p urpose of the present investigation was to determine the effects of time el apsed since treatment on the frequency of hprt mutant T-cells (Mf) from mic e treated transplacentally with single acute vs. multiple split doses of EN U. To this end, pregnant C57BL/6 mice (n = 13-16/group), which had been bre d to C3H males, were given i.p. injections of 40 mg ENU/kg bw in a single d ose on day 18 of gestation, in a split dose of 6 mg ENU/kg bw on days 12 th rough 18 of gestation, or DMSO vehicle alone. Groups of pups were necropsie d on days 10, 13, 15 (single dose only), 17, 20, 40, and 70 postpartum for T-cell isolations and hprt Mf measurements using the T-cell cloning assay. The time required to reach maximum Mfs in T-cells isolated from thymus of t ransplacentally treated animals was 2 weeks, the same time span as previous ly observed after ENU treatment of adult, weanling, and preweanling mice, M fs in T-cells isolated from spleens of control animals averaged 2.1 +/- 0.3 (SE) x 10(-6). In spleens of mice treated transplacentally with ENU in a s ingle dose, Mfs reached a maximum at 15 days postpartum [84.7 +/- 15.8 (SE) x 10(-6)] and decreased to lower but still elevated levels at 40 clays pos tpartum. In spleens of mice treated transplacentally with ENU in a split do se, Mfs reached a maximum at 13 days postpartum [74.0 +/- 16.3 (SE) x 10(-6 )] and decreased to background levels at 40 days postpartum. The areas unde r the curves describing the change in hprt Mfs over time for ENU-treated vs . control mice estimate the mutagenic potency for transplacental single- an d split-dose exposures to be 1.9 and 0.8 x 10(3), respectively. Comparison of the mutagenic potency estimates for mice exposed to ENU in utero to 4-we ek-old mice given a similar dose of the same lot number of ENU indicates th at the mouse is more susceptible to ENU-induced mutagenesis during fetal li fe. (C) 2001 Wiley-Liss, Inc.