Objective To investigate the effect of partial bladder outlet obstruction on detrusor blood¯ow and oxygen tension (PdetO 2 ) in female pigs. Materials and methods Detrusor-layer oxygen tension and blood¯ow were measured using oxygen-sensitive electrode and radiolabelled microsphere techniques in ®ve female Large White pigs with a partial urethral obstruction and in ®ve sham-operated controls. The effects of chronic outlet obstruction on bladder weight, and cholinergic nerve density and distribution, are also described. Results In the obstructed bladders, blood¯ow and oxygen tension were, respectively, 54.9% and 74.3% of control values at low bladder volume, and 47.5% and 42.5% at cystometric capacity. Detrusor blood¯o w declined by 27.8% and 37.5% in the control and obstructed bladders, respectively, as a result of bladder ®lling, whilst PdetO 2 did not decrease in the controls, but fell by 42.7% in the obstructed bladders. Bladder weight increased whilst cholinergic nerve density decreased in the obstructed animals. Conclusion In pigs with chronic bladder outlet obstruction, blood¯ow and oxygen tension in the detrusor layer were lower than in control animals. In addition, increasing detrusor pressure during ®lling caused signi®cantly greater decreases in blood¯ow and oxygen tension in the obstructed than in the control bladders.

Our study supports the notion that there is a fundamental abnormality in IDI at the level of the bladder wall, with evidence of altered spontaneous contractile activity consistent with an increased electrical coupling of cells, a patchy denervation of the detrusor and a potassium supersensitivity.

Bladder outflow obstruction is associated with repeated episodes of prolonged detrusor ischemia which may account for the biochemical and neuronal alterations in such bladders.

The pig model proved to be well suited to the experimental conditions and provided reproducible results. The principal determinant of blood flow within the wall of the bladder is the pressure within its lumen. During normal filling the blood supply of the bladder is able to adapt to the large increase in surface area which occurs, maintaining blood flow until the pressure increases.