Trypan blue accumulation in the embryonic gut of rats and mice during the teratogenic phase

Four to 48 hours after iv and sc administration of teratogenic doses of trypan blue to rats and mice the uterus was removed and rapidly frozen, after having been placed in a horizontal plane, and frozen sections were attached to tape and dried at a low temperature. By this procedure embryos and placental structures were present in the same sections and loss or redistribution of the dye was minimized. The dye was found in the yolk-sac cavity and to be accumulated in the visceral (proximal) endoderm. It was also acculmulated in the embryonic endoderm--forming the embryonic gut. This accumulation occurred after the administration of the trypan blue up to the time of closure of the vitelline duct, which occurs at 11 days postconception in rats and 9.5 days in mice. None was found when injection was made after this closure. No dye was detected in the ecto- and mesodermal layers. The period of embryonic uptake of trypan blue largely corresponds with the period of teratogenic sensitivity in these species as reported by others.