Abnormalities induced in cultured rat embryos by hyperthermia

Rat embryos were explanted at nine and one-half days of gestation and cultured for 48 hours in rotating bottles containing rat serum and a gas phase, at temperatures of 38, 40, 40.5 and 41 degrees C. The embryo cultured at 40.5 degrees C were retarded and many of them were abnormal, and at 41 degrees C, all the embryos were malformed and retarded. The most frequent abnormalities occurring at both these temperatures were microcephaly and oedema of the pericardium. Development of the embryos cultured at 40 degrees C was similar to that of the controls at 38 degrees C, and superficially they appeared to be normal. However, measurement of the head dimensions, and separate determinations of head and body protein contents showed that the 40 degrees C embryos were microcephalic.