TRPA1 receptor induced relaxation of the human urethra involves TRPV1 and cannabinoid receptor mediated signals, and cyclooxygenase activation.

OBJECTIVE

We studied whether TRPA1 agonists interact with sensory and inflammatory signals to relax human urethral smooth muscle.

METHODS

Urethral specimens were obtained perioperatively from 19 patients, and prepared for immunohistochemistry and functional experiments. The effects of allyl isothiocyanate, cinnamaldehyde and NaHS were studied in phenylephrine activated preparations combined with capsaicin, capsazepine, N omega-nitro-L-arginine, indomethacin or CP55940.

RESULTS

TRPA1, cannabinoid 1 and cannabinoid 2 immunoreactivity was colocalized in nerve fibers of the human urethra. All TRPA1 agonists produced relaxation of phenylephrine contracted urethral preparations. Capsaicin increased relaxant responses to all TRPA1 agonists. It increased the mean +/- SEM -logIC50 of cinnamaldehyde and NaHS from 4.91 +/- 0.26 to 5.15 +/- 0.22 and 3.27 +/- 0.14 to 3.79 +/- 0.35, and the -logIC30 of allyl isothiocyanate from 3.11 +/- 0.24 to 3.41 +/- 0.26 (each p <0.05). Capsazepine in 5 preparations, indomethacin in 6 and CP55940 in 5 decreased cinnamaldehyde mediated relaxation by up to 39%, 88% and 89%, respectively. Nomega-nitro-L-arginine and urothelial removal had no effect on relaxation by cinnamaldehyde in 5 preparations.

CONCLUSIONS

Relaxation to TRPA1 agonists in human urethral preparations seem to work in cooperation with TRPV1 mediated signals, are negatively coupled via cannabinoid receptor activation and involve cyclooxygenase products. Urothelial TRPA1 signals may not be important to regulate normal human urethral smooth muscle tone. This does not exclude a role in the initiation of afferent activity normally and in disease states.