Effects of short‐term partial bladder outlet obstruction on the rabbit detrusor: An ultrastructural study

It has been shown previously that partial bladder outlet obstruction in the rabbit results in changes in detrusor contractility and biochemical profile [Malkowicz et al., 1986]. The present study was conducted in the same animal model to define the nature and evolution of concomitant structural neuromuscular changes in the detrusor, as the basis for its altered function following partial outlet obstruction. Twenty‐five New Zealand White rabbits, including three normal controls, were used. The bladder was excised in 15 rabbits at various intervals 1–14 days postoperatively. In the remaining seven rabbits, the obstruction was relieved after 7 days, and the bladders were excised 14 or 28 days later. Multiple samples of the midbody detrusor were obtained from each specimen and processed for electron microscopy by standard techniques. Changes were observed in the smooth muscle, interstitial, and neural compartments. The muscular changes included a combination of muscle cell degeneration and regeneration, and widening of intercellular spaces with deposition of basal lamina‐like material. Both degenerative and regenerative muscle cell profiles were uncommon in the control and 1 day obstructed samples, frequent in the 3–7 day obstructed samples, and less frequent in the 14 day obstructed samples. The spaces between individual muscle cells appeared to become increasingly wider in the 3–14 day obstructed samples. The ultrastructure of smooth muscle in samples from both deobstructed groups was similar to controls, except for thickened basal laminae of muscle cells and consistently widened intercellular spaces. The interstitial compartment appeared to become progressively exaggerated with increasing deposits of collagen and elastin in the 3–14 day obstructed samples; these changes persisted in samples from both deobstructed groups. In regard to the neural compartment, degeneration of both cholinergic and adrenergic nerves with loss of neuroeffector junctions was observed in the 3–7 day obstructed samples; axonal regeneration was seen with re‐establishment of the junctions in the 14 day obstructed and both deobstructed groups. It is concluded that partial bladder outlet obstruction in the rabbit results in partially reversible neuromuscular changes in the detrusor, which can explain the resultant alterations in detrusor contractility and biochemical profile.