Effect of urethane anesthesia on the micturition reflex in capsaicin-treated rats

Cystometry was performed on rats with a chronically implanted intravesical catheter (2 days before cystometry) before and after induction of urethane-anesthesia. Four groups of animals were investigated: group A, vehicle-treated; group B, capsaicin-treated as adults (50 mg/kg s.c.) 4 days before cystometry; group C, capsaicin-treated as adults (125 mg/kg s.c.) 4 days before cystometry; and group D, capsaicin-treated as newborns (50 mg/kg) 2 months before. Rats of group D had a markedly enlarged bladder. Before induction of urethane anesthesia, the bladder capacity of rats of groups A, B and C was not significantly different from each other, while that of rats of group D was larger than controls. After induction of anesthesia bladder capacity in groups B and C was significantly increased as compared to group A and micturition was abolished in group D (overflow incontinence). Amplitude of micturition contraction was significantly reduced in all groups after induction of anesthesia but was unaffected by capsaicin pretreatment. It is concluded that the facilitatory action of capsaicin-sensitive nerves on micturition threshold is more evident in anesthetized than awake rats and that capsaicin-resistant bladder afferents are more sensitive to the depressant action of urethane than the capsaicin-sensitive ones.