The effects of D- and L-threo-chloramphenicol on the early development of the chick embryo

ABSTRACT In the presence of 200-300 μg./ml. of D-threo-chloramphenicol, chick embryos explanted at the full streak to head-fold stage develop abnormally. In the presence of the same and higher concentrations (600 μg./ml.) of the L-isomer, development is almost normal. The most obvious features of the response to D-threo-chloramphenicol are a failure of the neural tube to close and an inhibition of haemoglobin formation. In order to inhibit haemoglobin formation in the area vasculosa, it is necessary to treat the embryos several hours before the haemoglobin would appear. The abnormalities are accompanied by a reduction in the area of the blastoderm and of the area vasculosa. A high concentration of the L-threo compound, although it does not produce the embryonic abnormalities, does reduce the size of the blastoderm. The failure of the L-isomer to give rise to the abnormalities caused by the D-isomer suggests that the teratological response is due to an inhibition of protein synthesis caused primarily by an interference with the function of messenger RNA.