NEW ASPECTS OF MICROVASCULAR CORROSION CASTING - A SCANNING, TRANSMISSION ELECTRON, AND HIGH-RESOLUTION INTRAVITAL VIDEO MICROSCOPIC STUDY

We used intravital microscopy of small intestine and pancreas in order to show dynamic interactions between vascular wall and undiluted Merc er, because previous studies of ours have shown that Mercer diluted wi th monomeric methylmethacrylate penetrates cells in the vascular wall. Scanning and transmission electron microscopy were used to show three -dimensional pathways and correlating tissue structures, which cannot be identified in vivo. The microvascular diameters were not altered wh en the vasculature was flushed with saline/dextran solution using perf usion pressures between 70 and 140 mm Hg, but, in circumscribed areas, contraction of vascular wall was observed immediately after Mercer in jection. This phenomenon was carried out by endothelial cells; pericyt es were never present at the site of constrictions. Extravasation, i.e ., leakage of the resin into the surrounding tissue, occurred in circu mscribed areas regardless of the applied perfusion pressure. The resin also filled routes, which were not perfused with blood before casting . Scanning microscopy of corresponding specimens showed flattened cast channels, with impressions of valves and endothelial cell nuclear imp rints characteristic of lymphatics. These results show that undiluted Mercer is a stimulus for vascular cellular components and that it chan ges the vascular wall permeability, resulting in extravasation and fil ling of lymphatics. Transmission electron microscopy showed that large vessels were homogeneously filled with resin and that cellular struct ures were not infiltrated with Mercer. Cut sections of the gold-coated surface of casts showed grooves up to 20 nm wide, suggestive of minim al deformation, while the abluminal surface of the metal film was almo st smooth. Another proof of minimal deformation of undiluted Mercer ca sts is that the diameter of vessels was not altered during and after p olymerization. Obtained casts are not fragile, as are casts of diluted Mercer, and phase separation does not occur, which would result in pe netration of the cells in the vascular wall. For these reasons, the us e of undiluted Mercer is recommended. Mixing 10 ml Mercer with 1 g cat alyst resulted in complete polymerization within 5.5-7 min. This mixtu re can be used for casting biological specimens. (C) 1993 Wiley-Liss, Inc.