EVIDENCE FOR A UNIQUE ELASTIC SHEATH SURROUNDING THE VESICULAR ARTERIES OF THE RABBIT URINARY-BLADDER - STUDIES OF THE MICROVASCULATURE WITH MICROSCOPY AND VASCULAR CORROSION CASTING

Because the urinary bladder stores and releases urine, its normal func tion includes filling and emptying, accompanied by distension and rela xation. It is known that chronic distension compromises blood flow. Re cent studies of the rabbit bladder vasculature have described speciali zations of that vasculature that appear to enhance blood flow in the b ladder wall during distension. The present report describes the locati on, orientation, and structure of an elastic sheath surrounding the ve sicular arteries, which may represent one of these specializations. Th e location, vasculature, and structure of an accessory elastic sheath surrounding the vesicular arteries of the rabbit bladder is described using light and electron microscopy, India ink injection, and vascular corrosion casting. The common iliac arteries of rabbits were cannulat ed to permit perfusion of the distal vasculature including the urinary bladder. After the bladder vasculature was visually cleared of blood by perfusion with buffered saline, one of the following procedures was used: 1) for Light or electron microscopy, the bladder was perfuse-fi xed with buffered 2% glutaraldehyde; 2) the bladder vasculature was fi lled with India ink for vessel tracing; or 3) corrosion casts of the b ladder vasculature were prepared by infusion of a Mercer resin mixture . Casts, cleaned of tissue with KOH, and water and formic acid rinses, are dried, and mounted for routine scanning electron microscopy. The presence of an accessory sheath surrounding the main vesicular arterie s and some of their branches in the basal two thirds of the urinary bl adder was observed on India ink injected specimens and confirmed by mi crographs and vascular corrosion casts. The sheath consists of elastic and collagenous fibers and is separated from the tunica media of the arteries by a loose connective tissue layer of variable width. The she ath is circumscribed by a layer of fine blood vessels. The vesicular a rteries undulate within the sheath to an extent which is dependent upo n the degree of distension of the bladder. This sheath likely represen ts a specialization which permits the bladder vasculature to accommoda te expansion and contraction of the wall during normal filling and emp tying. Undulations or coiling of the vesicular arteries within the loo se connective tissue core of the sheath increase with bladder contract ion, and apparently the sheath simply holds the artery in position dur ing such coiling. The sheath, may represent a modification of the exte rnal elastic lamina found in some muscular arteries. Anat. Rec. 252:47 2-476, 1998. (C) 1998 Wiley-Liss, Inc.