Effect of distension on function and nervous ultrastructure in the canine urinary bladder

Canine bladders were distended for 4 h at 100 cm H2O to study the effects of distension on bladder function and structure. A micturition study was performed before overstretching, immediately after distension and 5 days after it. Bladder function was impaired immediately after distension, compliance and residual urine were increased and the maximum pressure during voiding decreased. The function returned to normal after 5 days. Overstretching caused diffuse or focal submucosal haemorrhages, only rarely fibrosis or necrosis of bladder wall. Electron microscopic changes of the bladder peripheral nerves were slight, the consistent finding being oedema in areas of outer mesoaxons and between cytoplasmic processes of Schwann cells. This change was sometimes accompanied by a rupture of the surrounding basement membrane. Axonal lysis was observed in one case. It is concluded that these anatomical changes, although found at the moment of functional recovery, may be linked to impaired conductivity of nerves in the bladder wall causing, at least partly, its impaired function. This may further decrease bladder instability and after urinary retention cause prolonged micturition problems. Functional recovery occurs, however, quite rapidly in healthy bladders.