Acquired urinary incontinence in the bitch (AUI) is currently reported to affect 20% of neutered bitches and <1% of intact bitches and males; however the full aetiology of the condition remains unknown.

Our previous in vitro study demonstrated that neutering is associated with a decrease in response to muscarinic stimulation of the detrusor muscle in the canine, independent of gender. The aim of this study was to investigate whether neutering altered the expression of mRNA for M1 and M2 receptors in the bladder wall.

Sections of bladder wall were dissected post mortem from entire and neutered male and female dogs (ME, MN, FE, FN respectively) with informed owner consent. RNA was extracted; reverse transcribed and M1, M2 mRNA expression quantified by rtPCR (relative to β-actin).

Table1. Relative expression levels of mRNA, presented as mean ± s.e. mean where n = number of dogs.

Analysis of variance (Bonferroni post-test) show M1 and M2 mRNA expression was significantly (p<0.05) decreased in male compared to female animals, and significantly increased in neutered compared to entire animals (M1 both sexes, M2 males only).

These results demonstrate that neutering a dog is associated with increased M1 and M2 mRNA expression in the bladder. These dynamic changes indicate differential mechanisms through which neutering and gender may influence bladder responsiveness and thus AUI.