SOME HISTOCHEMICAL OBSERVATIONS ON TRANSITIONAL EPITHELIUM OF MAN

This report deals with a histochemical characterization of transitional epithelium of the urinary tract of man. The cytoplasm of cells of the innermost, luminal layer is distinctly stained by the periodic acid-Schiff procedure. Enhanced staining of the luminal border of these cells suggests the presence of a differentiation of the luminal surface ( surface mucous coat) which is selectively stained by Alcian Blue and colloidal iron. The alcianophilic surface mucous coat is seen in the innermost layer of transitional epithelial cells of the urinary tract extending from the area cribrosa down to the bladder. This indicates the presence of an acid mucinous component. Digestion with neuraminidase according to the procedure of Spicer and Warren demonstrates the presence of N-acetylneuraminic acid (sialic acid) in the free cell surface of the luminal layer of transitional epithelium of man. There is abundant glycogen in transitional epithelium of man. A very characteristic basement membrane underlies transitional epithelium. It reacts with periodic acid-Schiff and often with Alcian Blue. The neuraminidase digestion does not alter the staining of basement membrane with Alcian Blue. This suggests the presence of a sialidase-resistant form of sialomucin or a sulfomucin in basement membrane. The presence of periodic acid-Schiff-positive, nondigestible granules closely corresponds to acid phosphatase-reactive granules, presumably lysosomes. Within the transitional epithelium there were lacunae which contained abundant sialomucins. These structures have been described in old textbooks of histology but do not seem to be a normal component of transitional epithelium. The significance of these structures is unknown.