Developmental toxicity study of tetramethylurea (TMU) in rats

The developmental toxicity of tetramethylurea (TMU) was assessed in rats by inhalation exposure of the test material over days 6-20 of gestation. Grou ps of 25 mated female Crl:CD (R) BR rats were exposed whole-body for 6 hour s/day to concentrations of either 0, 2, 20 or 100 ppm TMU. The dams were eu thanized on day 21 and the offspring were weighed, sexed, and examined for external, visceral, and skeletal alterations. Maternal toxicity was demonst rated at both 20 and 100 ppm. Maternal body weights, weight changes, and fo od consumption were statistically significantly reduced at these concentrat ions: effects were more pronounced at 100 ppm. There was evidence of develo pmental toxicity only at 100 ppm. The only finding was a decrease in mean f etal weight. No fetal malformations or variations occurred in fetuses deriv ed from rats exposed to all 3 test concentrations (up to 100 ppm). The mate rnal no-observed-effect-level (NOEL) was 2 ppm. the fetal NOEL was 20 ppm. Thus, TMU was not considered to be uniquely toxic to the rat conceptus.