MICROVASCULATURE OF THE RABBIT URINARY-BLADDER

Background: The urinary bladder requires a rich blood supply to mainta in its functions, the storage and release of urine. Specialized proper ties of the bladder vasculature might be anticipated to ensure the int egrity of this blood supply, because it is known that blood flow is re duced by distension during bladder filling. However, the bladder vascu lature has been described in detail only at the gross level. A compreh ensive, three-dimensional view of the blood supply to the bladder wall is presented here. Methods: The microvasculature of the bladder of ma le New Zealand white rabbits was described using the combination of va scular corrosion casting, alkali digestion, light microscopy, and scan ning and transmission electron microscopy. Following administration of an anticoagulant and an overdose of anesthetic, the abdominal aorta w as cannulated just above the inferior mesenteric artery to permit flus hing of the distal vasculature. The bladder vasculature was cleared of blood with buffered saline and then either perfuse-fixed with buffere d 2% glutaraldehyde and sectioned, or filled with ''Mercox'' resin to prepare vascular corrosion casts. Casts were cleaned with NaOH, formic acid, and water. In some cases fixed bladders were partially digested with NaOH to expose the mucosal capillary plexus. Results: The bladde r is supplied with blood by single, left and right vesicular branches of the internal or external iliac arteries. The serpentine vesicular a rteries extend along the lateral borders of the bladder from base to a pex just deep to the serosal surface and send dorsal and ventral branc hes to supply the dorsal and ventral bladder walls. Veins accompany th e arteries and exhibit numerous valves. A very dense complex of vessel s at the apex of the bladder apparently serves to accommodate bladder distension. The muscularis and submucosa contains few vessels, but the mucosa is well vascularized. An especially dense capillary plexus is present in the lamina propria at its junction with the transitional ep ithelium. In the relaxed bladder these capillaries lie in grooves form ed by the basal layers of the epithelium. The endothelial cells of the se capillaries display few cytoplasmic vesicles and are continuous or fenestrated. These capillaries are often invested with pericytes. The mucosal capillary plexus may be associated with an epithelial transpor t function or may be necessary for urothelial metabolism or maintenanc e of the barrier function of the urothelium. Unusual capillary tufts, possibly associated with vascular lymphatic tissue, are found associat ed with the main vessels on the lateral walls in the basal half of the bladder. Conclusions: These methods present a clear, comprehensive, t hree-dimensional view of the microvasculature of the bladder wall. The y also identify several unique features of this vasculature and provid e a basis for studies of the response of this vasculature to pathologi c states and experimental manipulation. (C) 1995 Wiley-Lies, Inc.