Microinfusion method using barium sulfate for visualization of embryonic blood vessels with light and scanning electron microscopy.

An X-ray contrast medium commonly used for clinical examination of the gastrointestinal tract was purified and applied as an injectant for the observation of the blood vasculature maturing in an early embryonic stage of the mouse. The embryos were perfused with the injectant through the umbilical cord and were processed for light and scanning electron microscope (LM and SEM) observations. When infused, the vessels turned white, the color of barium sulfate, thereby the adequate injection pressure and the amount of the injectant were readily controlled. The whole vasculature of the embryo was elucidated with an SEM in great detail at 9.5 days of the embryonic stage, four days earlier than previously achieved with a resin injection. The back scattered electron image of the lung alveolar capillaries containing barium sulfate was successfully obtained with an SEM in the 17.5 day embryo. The backscattering image and the secondary electron image of the identical area were compared to elucidate the spatial relationship between the capillaries and their circumferential cells such as type I and type II alveolar cells. The vascular injection with barium sulfate introduced may facilitate the systemic study of the blood vasculature and may provide useful information as to the relationship vascular formation and organogenesis occurring in an early embryonic stage.