Improved technique for fetal heart examination in developmental toxicity studies in rats.

Bouin's or a 10% formalin solution has been used to fixate internal fetal observations for developmental toxicity studies in rats. However, these fixatives are known to cause contraction of the ventricle of the heart and arteries, which makes dissection and observation more difficult. Fetuses on day 20 of gestation from pregnant Crj:CD(SD)IGS rats were injected with 10 w/v% magnesium chloride/10 vol% neutral buffered formalin solution into the thoracic cavity, and then fixed in 10 vol% neutral buffered formalin. After fixation, the heart was dissected using a modified Staples technique. In treated fetuses, the membranous region of the ventricular septum and the valves were clearly observed in an expanded state. We conclude that this method increases the ability to detect heart anomalies and decreases the chance of a false-positive finding.