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Corrosion casting is an important tool for the study of microvascular structure, but unlike tissue preparation for light and electron microscopy, few controlled studies of the methods for preparation of microvascular casts for scanning electron microscopy have been reported. Most vascular casting begins with rinsing cells from the lumen of the blood vessels, but the necessity of this has not been shown. Because of a report of successful casting without rinsing and light microscopic evidence of edema with complete rinsing prior to casting, this preparation procedure was examined. Casts of lung vasculature that were thoroughly rinsed were compared to those that were not. Of the six rats that were not lavaged, only one gave a completely filled cast, but of the six animals that were well rinsed, only one did not fill. Except for the filling and mild periarterial edema, no significant difference in cast quality or features was detected. Rinsing improves the frequency of obtaining completely filled casts. The edema does not greatly interfere with the capillary image and its location gives insight into this process in the lung.

To determine the importance of the pulmonary or bronchial arteries as the site of injection to cast the lung vasculature of rats, we retrospectively compared a group of normal Sprague-Dawley rats that were cast through either the caudal vena cava and right ventricle leading to the pulmonary arteries or through the aorta and bronchial arteries. There was no difference in the appearance of the whole casts or cast-to-lung weight ratios between the two groups, although an incompletely cast lung that was injected through the aorta showed preferential filling of the pleural and peribronchial regions. Nuclear impressions, a sign of good filling, were more frequent and the grade of the images was higher in the group filled through the vena cava. The microvascular density index was not different between the two groups, and a multivariate analysis of variance showed the injection site was not important in determining vascular density. The pulmonary vessels fill nearly as well when injected from the bronchial circulation indicating that the bronchial circulation can immediately perfuse the lung if the pulmonary arteries are obstructed, and casting can be carried out from either side with nearly the same results.