Effect of cryoinjury on the contractile parameters of bladder strips: A model of impaired detrusor contractility

In anesthetized Sprague-Dawley rats, the bladder was exposed and cryoinjury was induced by abruptly freezing the serosal side of the bladder wall with a chilled aluminum rod previously placed on dry ice (-40 degrees C). Five days later, the rats were euthanized, and strips were prepared from the area adjacent to the injury. Neurally and alpha,beta methylene-ATP (alpha,beta m-ATP; 50 microM)-evoked contractions were measured in bladder strips from cryoinjured or intact bladders prepared from sham-operated rats. Cryoinjured bladder strips produced significantly lower contractile forces than intact strips to electrical stimulation at higher (10-40 Hz) frequencies. The maximal rate of the neurally evoked contractions was slower in the cryoinjured bladders. The contractile response to alpha,beta m-ATP was smaller in the cryoinjured preparations indicating that the changes may have also occurred at the postjunctional site. In addition, atropine was more effective at inhibiting the neurally evoked contractions in the cryoinjured bladder strips suggesting that a cholinergic dominance occurs after cryoinjury. It is concluded that cryoinjury is a viable method of causing a defined, reproducible injury to the urinary bladder resulting in impaired function of both the cholinergic transmission and the smooth muscle. The bladder cryoinjury can be used as a model for studying impaired bladder compliance and detrusor contractility as well as treatments that may improve bladder function such as tissue engineering.