Neutering affects urinary bladder function by different mechanisms in male and female dogs.

Acquired urinary incontinence is a significant, incurable problem, prevalent in neutered bitches but rarely seen in entire bitches or males. Decreased urethral closure pressure has been proposed as a causative factor for altered detrusor contractility in the neutered bitch. In post menopausal women, acquired urinary incontinence is associated with acquired urinary incontinence and changes in collagen deposition within the bladder wall. The aim of this study was to determine effects of neutering on smooth muscle in the canine urinary bladder. Tissue bath studies were used to assess contractile function and morphometric analysis to determine percentage of collagen in the bladder wall from male and female, neutered and entire canines. Maximal response to both carbachol and neurogenic stimulation was significantly lower in bladder strips from neutered animals of both sexes. Sensitivity to carbachol was also significantly reduced by neutering in both sexes. The percentage of collagen was significantly higher in the bladder wall from neutered vs. entire females, which were similar to that of both neutered and entire males. Neutering a canine decreases urinary bladder responsiveness to muscarinic stimulation in vitro, in both sexes, but only increases the percentage of collagen in the bladder wall in females. While increased percentage collagen may predispose bitches to acquired urinary incontinence, the sex difference in this parameter indicates that more than one mechanism underlies the changes in bladder responsiveness seen following neutering. This alternative effect of neutering may be in the muscarinic receptor effector pathway and act as a therapeutic target for acquired urinary incontinence treatment.