Specific teratogenic action of 2,4,5-trichlorophenoxyacetic acid on mouse and rat whole-embryo cultures

The effects of 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) were studied at concentrations ranging from 0.17 to 3.52 m m on post-implanted mouse and rat embryos cultured for 48 hr, either in the absence of any metabolic activation system or in the presence of mouse and rat S-9 mix. 2,4,5-T proved to be a potential teratogen, at 0.88 and 1.76 m m, on mouse embryos in the absence of any metabolic activation system. In the presence of mouse S-9 mix, 2,4,5-T showed a high teratogenic potential at 0.17, 0.88 and 1.76 m m. In contrast, in the presence of rat S-9 mix, 2,4,5-T induced structural defects only at 1.76 m m. At 3.52 m m, 2,4,5-T was 100% embryolethal with or without S-9 mix. On rat embryos, 2,4,5-T was potentially teratogenic only in the presence of mouse S-9 mix, causing a significant increase in dysmorphogenic effects at 0.17, 0.88 and 1.76 m m. With or without rat S-9 mix, 2,4,5,-T was only embryolethal to rat embryos at 1.76 and 3.52 m m. The abnormalities mainly involved the forebrain, the midbrain and the branchial arches. These results are consistent with the known in vivo embryotoxic action of this compound.