Intravascular
injections of fluorescent or biotinylated
tomato lectin were tested to study labeling of vascular elements in laboratory mice.
Injections of Lycopersicon esculentum
agglutinin (
tomato lectin) (50-100 µg/100 µl) were made intravascularly, through the tail vein, through a
cannula implanted in the jugular vein, or directly into the left ventricle of the heart. Tissues cut for thin 10- to 12-µm cryostat sections, or thick 50- to 100-µm vibratome sections, were examined using fluorescence microscopy. Tissue labeled by biotinylated
lectin was examined by bright field microscopy or electron microscopy after tissue processing for
biotin. Intravascular
injections of
tomato lectin led to labeling of vascular structures in a variety of tissues, including brain, kidney, liver, intestine, spleen, skin, skeletal and cardiac muscle, and experimental
tumors. Analyses of fluorescence in serum indicated the
lectin was cleared from circulating blood within 2 min. Capillary labeling was apparent in tissues collected from animals within 1 min of intravascular
injections, remained robust for about 1 h, and then declined markedly until difficult to detect 12 h after injection. Light microscopic images suggest the
lectin bound to the endothelial cells that form capillaries and endothelial cells that line some larger vessels. Electron microscopic studies confirmed the labeling of
luminal surfaces of endothelial cells. Vascular labeling by
tomato lectin is compatible with a variety of other morphological labeling techniques, including histochemistry and immunocytochemistry, and thus appears to be a sensitive and useful method to reveal vascular patterns in relationship to other aspects of parenchymal development, structure, and function.