Influence of nitric oxide signalling pathways on pre‐contracted human detrusor smooth muscle in vitro

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Abstract
Objectives To assess the effects of nitric oxide (NO) donors on human detrusor strips in vitro under conditions which attempt to mimic those occurring in vivo during the tonic phase of bladder contraction, as NO may promote relaxation by modulating parasympathetic excitation contraction coupling. Materials and methods With ethical approval from the local ethics committee, human detrusor tissue was obtained from a heterogeneous clinical group after obtaining informed consent. Detrusor strips were dissected and mounted in a 1‐mL, superfused organ bath. After pre‐contraction with carbachol, the effect of NO donors, sodium nitroprusside (SNP) and S‐nitro‐N‐acetylpenicillamine, a cell‐permeable cyclic nucleotide analogue (dibutyl‐cGMP), and inhibitors (methylene blue and ibuprofen) on isometric tension were assessed. All drugs were dissolved in Tyrode solution (pH 7.4), passed through a thermostatically controlled (36 °C) warming jacket and bubbled with 95% O2/5% CO2. Results Both NO donors and db‐cGMP evoked a complex response in pre‐contracted tissue, i.e. relaxation, contraction or a transient relaxation followed by contraction. Inhibition of soluble guanylyl cyclase significantly attenuated NO‐mediated contraction, indicating the involvement of cGMP, but this inhibition did not significantly affect the relaxant response. The relaxant response was also potentiated by ibuprofen. SNP and db‐cGMP evoked similar responses, although the occurrence of the responses (relaxation, contraction or biphasic) was significantly different in normal and pathological human detrusor. Conclusion NO donors and db‐cGMP modulate carbachol‐evoked contraction of human detrusor smooth muscle in vitro. There is probably a NO/cGMP signalling pathway, with inhibition of endogenous cGMP by methylene blue, suggesting that SNP evokes contraction via cGMP. However, NO donors and db‐cGMP evoked a complex response (relaxant, contractile or biphasic), suggesting that NO and cGMP may also act independently and/or via several pathways.