Inhibitory effect of capsaicin on detrusor contractility: Further study in the presence of ganglionic blocker and neurokinin receptor antagonist in the rat urinary bladder

In order to understand the mechanisms by which capsaicin at high concentrations affects the micturition reflex and detrusor contractility, in vivo and in vitro whole bladder studies were conducted using ganglionic blockers and a neurokinin receptor antagonist. Thirty-eight adult rats were divided into control (normal saline cystometry) and experimental (1,000 mu M capsaicin cystometry) groups. Both groups were subdivided to receive pretreatment with intravesical hexamethonium, perivesical hexamethonium, or intravesical spantide ([D-Arg(1), D-Trp(7,9), Leu(11)]-substance P). After in vivo cystometry, the bladders were removed and in vitro whole bladder contractility studies using electrical field stimulation as well as bethanechol and KCl stimulations were performed. In the bladders pretreated with perivesical hexamethonium, the amplitudes of contractions and in vitro detrusor contractility under electrical stimulation were decreased. Other bladder preparations showed no significant differences from the controls. However, when 1,000 mu M capsaicin was infused into the bladders, both control and experimental bladders showed an initial excitation and a final inhibition with an elevated basal intravesical pressure and retention. Capsaicin at 100 mu M did not have this effect. The results of this study conclude that blockage of perivesical ganglia or neurokinin receptors in the submucosa did not influence the depressant effects of 1,000 mu M capsaicin on the micturition reflex and detrusor contractility in rats. Nonspecific toxic effects on detrusor muscle or nerves is likely when intravesical high-concentration capsaicin is administered.