Application of fluorescence densitometry to the study of net albumin uptake by the rabbit aortic wall up- and downstream of intercostal ostia.

A method was developed for measuring levels of lissamine rhodamine B-labelled albumin in arterial walls with a spatial resolution of ca. 1 micron 3. The method was used to study variation in net macromolecular uptake up- and downstream of intercostal ostia in a small number of rabbit aortae. The physical and biological properties of the fluorescent tracer, including its stability, were compatible with its use in vivo. Tracer was injected into the ear vein of conscious rabbits. After 3 h the rabbits were anaesthetized and the thoracic aorta was fixed in situ at physiological pressure. The vessel was embedded in epoxy resin and longitudinal sections of the aortic wall were cut through the centre of the intercostal ostia. Photomicrographs were used to record fluorescence from these sections. The optical density across the photomicrographs was measured and related to the distribution of tracer in the wall. Mean intima-medial levels of tracer were greater downstream of ostia than upstream but were lower near the flow divider than further downstream. Higher levels of tracer were found in the adventitia than in the media and, in the latter, the distribution appeared to be related to the lamellar structure.