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 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, 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. In contrast, in the presence of rat S-9 mix, 2,4,5-T induced structural defects only at 1.76 m. At 3.52 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. With or without rat S-9 mix, 2,4,5,-T was only embryolethal to rat embryos at 1.76 and 3.52 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.