Cytological and lectin histochemical characterization of secretion production and secretion composition in the tubular glands of the canine anal sacs

The study reports on secretion production and composition in the tubular gl ands of the canine anal sacs. For this purpose, light and electron microsco pical (TEM, SEM) as well as several histochemical methods for the demonstra tion of lysosomal acidity, lipofuscin, and complex carbohydrates were used. The glandular tubules exhibited a pseudostratified epithelium with secreto ry cells of a different shape as related to secretion production activity, and regionally varying amounts of basal cells. Flat, cuboidal or columnar c ells with or without apocrine-like protrusions were assembled in one glandu lar endpiece, although grouping of these cell types often occurred. Active secretory cells were columnar with many cytoplasmic vesicles and a typicall y merocrine and/or micro-apocrine exocytosis of vesicle contents. Additiona lly, many lysosomes of different sizes could be found, whereby in aged cell s giant secondary lysosomes (auto-phagolysosomes, about 7 mum in diameter) occupied the major cell part. These giant lysosomes were shed by an apocrin e-like process forming a final bottleneck stage of the upper cell part, and consisted of ceroid-type lipofuscin. The general carbohydrate histochemica l and the lectin histochemical methods revealed that the secretion produced was composed of strongly concentrated neutral glycoproteins with the follo wing saccharide residues: alpha -D-mannose, beta -D-galactose, beta -N-acet yl-D-glucosamine, alpha -L-fucose and N-acetyl-neuraminic acid (sialic acid ); the luminal secretion contained only beta -D-galactose and, especially, N-acetyl-neuraminic acid. This luminal secretion showed a spatially orienta ted maturation beginning in terminal tubular regions and finishing near the excretory duct, independent of the different secretory cell types. The res ults obtained demonstrated highly active secretion production, with a regio nal variation in the glandular tubule, and at least three different modes o f secretion by the secretory cells, whereby the shedding of giant lipofusci n granules seems to be very specific. The high amounts of sialic acids in t he glycoproteins found may influence the rheological properties of the secr etion by their water-binding capacities. Copyright (C) 2001 S. Kaiger AG, B asel.