TRPV1 is involved in stretch-evoked contractile changes in the rat autonomous bladder model: a study with piperine, a new TRPV1 agonist.

AIM: Vanilloids like capsaicin and resiniferatoxin (RTX) have been used for more than a decade in the treatment of neurogenic detrusor overactivity. Recently, the vanilloid molecule piperine (PIP) has been shown to have similar pharmacological properties as these drugs. In this study, we looked at PIP-effects on autonomous bladder contractile activity, with particular interest for its selectivity for the transient receptor potential channel 1 (TRPV1) receptor. Additionally, we studied the role of TRPV1 in volume-induced contractile changes using selective and non-selective TRPV1 antagonists.

METHODS: The acute and prolonged effects of PIP were studied on rat bladders. Each bladder was excised and placed in a heated organ bath, where intravesical pressures were measured. In acute experiments, PIP was added directly to the bathing solution. For prolonged effects, animals were pre-treated intravesically with vehicle (ethanol 5%) or PIP (10(-4) M) and sacrificed 72 hr later. The effects of selective (capsazepine (CZP)) and non-selective (ruthenium red (RR)) TRPV1 antagonists on volume-evoked contractile parameters were also studied.

RESULTS: Acute administration of PIP 10(-4) M significantly increased amplitude of bladder contractions (P < 0.05). These effects were significantly antagonized (P < 0.05) by the TRPV1-selective antagonist CZP (10(-5) M) and the non-selective TRP-antagonist RR (10(-5) M). Intravesical pre-treatment with PIP induced shorter contractions with more periods of non-activity (P < 0.05) compared to controls. Inhibition of TRPV1 with CZP and RR significantly reduced the volume-evoked rise in contractile amplitude in isolated bladders (P < 0.05).

CONCLUSION: We found evidence for acute and prolonged effects of PIP on bladder contractility, which seem to be mediated through TRPV1. Furthermore, we found evidence for involvement of TRPV1 in afferent signaling of mechanical stimuli.