Microvascular corrosion casting with analysis in the scanning electron microscope

The rat uterus was used as a microcirculatory model for an evaluation of different microvascular corrosion casting techniques. The two major variables determining the quality of casts were the degree of filling of the system cast and the replication of endothelial cells. A simple preparation of a low‐viscosity methyl methacrylate (η = 2–5 cS) was found superior to more viscous resins regarding both variables when infused at a physiological infusion pressure. Differential corrosion in 20% KOH and 5 M HCl at 40°C on a rotating rocker plate with intervening periods in distilled water and ultrasonic treatment was found the most effective corroding procedure. Acceptable conductivity for scanning electron microscopy could be achieved by osmium impregnation from used postfixation buffers, but sputter coating with a 400–10,000 A gold layer was the simplest and fastest method of rendering casts conductive. An arteriolar resistive mechanism not observed previously, segmental arteriolar spasm, was found on arteriolar casts. The imprints of endothelial cell nuclei could conveniently be described by their D/d ratio, that is, the quotient between the longest nuclear diameter and the diameter perpendicular to it. The arteriolar side of a capillary (ϕ 4–10 μm) exhibited arteriolar‐like endothelial cell nuclear imprints (D/d = 2.5–4), while its venular end showed venular‐like endothelial cell nuclear imprints (D/d = 1–1.5), making analysis of the direction of flow within capillary segments possible. “Plastic strips,” considered previously to indicate an avascular circulation in the media of arterioles were observed, and probably represented remnants of uncorroded smooth muscle cells. Localized extravasations of resin might have been caused by gaps between endothelial cells, but this interpretation was restricted to small (< 15 μm) extravasations from post‐capillary venules or capillaries in an area that is known ultrastructurally to possess interendothelial cell gaps.