Wall mechanics of the rat bladder. I. Hydrodynamic studies in the time domain.

The hydrodynamic properties of the rat bladder in the collection phase were examined by slow continuous and very fast stepwise cystometry in nine rats. In vivo, the fast volume steps induced a reproducible detrusor contraction (type A) which remained after spinal anaesthesia and anticholinergic treatment, but ceased post-mortally within 1 h. No significant effect of anticholinergic treatment was found on bladder stiffness. The stiffness and relaxation time of the bladder wall increased markedly at large distension. At small and moderate distension, however, the compliances evaluated from continuous and stepwise cystometry were nearly the same, and a linear elastic model of the bladder was applicable. We consider that the rat bladder will be a useful experimental model in further research on viscoelasticity and instability of the bladder wall.