Neutering affects mRNA expression levels for the LH- and GnRH-receptors in the canine urinary bladder

Neutering a bitch increases the incidence of acquired urinary incontinence (AUI) 20-fold. Mechanistically this effect is thought to be related to altered steroid/reproductive hormone concentrations and a recent study showed that gonadotrophin releasing hormone (GnRH) analogue treatment improved continence in bitches with AUI. The aim of this study was to examine mRNA expression levels for luteinizing hormone (LH)- and GnRH-receptors in the canine bladder and the correlation between these and in vitro contractility of the bladder using age matched entire and neutered, male and female canines and canines with AUI. Biopsies from the dome of the bladder were dissected post mortem with informed owner consent. mRNA expression for LH- and GnRH-receptor was quantified by rtPCR (relative to beta-actin). Contractility was assessed (cumulative concentration response curve for carbachol) in strips of bladder muscle using standard protocols. Analysis of variance (Tukey post-test) demonstrated thet neutering was associated with significantly increased levels of expression of LH- and GnRH-receptor mRNA in both sexes (P<0.01). mRNA expression for both receptors was significantly higher in female versus male canines. Neither effect was affected by animals' age and/or weight. A significant inverse correlation (Spearman's test) was found between bladder contractility and mRNA expression for both receptors. This effect was most pronounced in canines with AUI which demonstrated the highest mRNA expression levels yet had the lowest contractility of all animals studied. This suggests that increased LH- and GnRH-receptor mRNA expression is associated with changes in bladder function that increase an animal's predisposition to develop AUI.