Nonmucinous nature of the surface material of the bladder mucosa

The urinary bladder is lined by transitional epithelium, also known as urothelium. Some investigators have described a material known as mucin, which lines the luminal surface of the urothelium, but its nature is not well understood. The authors examined sections of bladder from rat, mouse, rabbit, and man and found that, although they reacted differently to common histochemical stains for complex carbohydrates, none showed any material that stained as mucin on the surface of the mucosa. Rather, intracellular granules that have varying staining characteristics in different animals were found on the luminal side of the urothelium. The authors speculate, based on their histochemical findings, that some form of mucin may be present in the urothelial granules in man and that studies on animals may not be applicable to man.