Background and purpose: As pituitary adenylate cyclase-activating polypeptide 38 (PACAP 38)-and vasoactive intestinal peptide (VIP) are widely distributed in the urinary tract, the current study investigated the receptors and mechanisms involved in relaxations induced by these peptides in the pig bladder neck. Experimental approach: Urothelium-denuded strips were suspended in organ baths for isometric force recordings and the relaxations to VIP and PACAP analogues were investigated. Key results: VIP, PACAP 38, PACAP 27 and [Ala 11,22,28 ]-VIP produced similar relaxations. Inhibition of neuronal voltage-gated Ca 2 þ channels reduced relaxations to PACAP 38 and increased those induced by VIP. Blockade of capsaicin-sensitive primary afferents (CSPA), nitric oxide (NO)-synthase or guanylate cyclase reduced the PACAP 38 relaxations but failed to modify the VIP responses. Inhibition of VIP/PACAP receptors and of voltage-gated K þ channels reduced PACAP 38 and VIP relaxations, which were not modified by the K þ channel blockers iberiotoxin, charybdotoxin, apamin or glibenclamide. The phosphodiesterase 4 inhibitor rolipram and the adenylate cyclase activator forskolin produced potent relaxations. Blockade of protein kinase A (PKA) reduced PACAP 38-and VIP-induced relaxations. Conclusions and implications: PACAP 38 and VIP relax the pig urinary bladder neck through muscle VPAC 2 receptors linked to the cAMP-PKA pathway and involve activation of voltage-gated K þ channels. Facilitatory PAC 1 receptors located at CSPA and coupled to NO release, and inhibitory VPAC receptors at motor endings are also involved in the relaxations to PACAP 38 and VIP, respectively. VIP/PACAP receptor antagonists could be useful in the therapy of urinary incontinence produced by intrinsic sphincter deficiency.

Background and purpose: As nitric oxide (NO) plays an essential role in the inhibitory neurotransmission of the bladder neck of several species, the current study investigates the mechanisms underlying the NO-induced relaxations in the pig urinary bladder neck. Experimental approach: Urothelium-denuded bladder neck strips were dissected and mounted in isolated organ baths containing a physiological saline solution at 37 1C and continuously gassed with 5% CO 2 and 95% O 2 , for isometric force recording. The relaxations to transmural nerve stimulation (EFS), or to exogenously applied acidified NaNO 2 solution were carried out on strips pre-contracted with phenylephrine, and treated with guanethidine and atropine, to block noradrenergic neurotransmission and muscarinic receptors, respectively. Key results: EFS (0.2-1 Hz) and addition of acidified NaNO 2 solution (1 mM-1 mM) evoked frequency-and concentrationdependent relaxations, respectively. These responses were potently reduced by the blockade of guanylate cyclase and were not modified by the K þ channel blockers iberiotoxin, charybdotoxin, apamin or glibenclamide. The voltage-gated K þ (Kv) channels inhibitor 4-aminopyridine, greatly enhanced the nitrergic relaxations evoked by EFS, but did not affect the NaNO 2 solution-induced relaxations. Conclusions and implications: NO, whose release is modulated by pre-junctional Kv channels, relaxes the pig urinary bladder neck through a mechanism dependent on the activation of guanylate cyclase, in which post-junctional K þ channels do not seem to be involved. Modulation of Kv channels could be useful in the therapy of the urinary incontinence produced by intrinsic sphincteric deficiency.

Results suggest that endogenous H2S synthesized by cystathionine γ-lyase and released from intramural nerves acts as a powerful signaling molecule in nitric oxide independent inhibitory transmission to the pig bladder neck.

The results suggest that PACAP 38, mainly released from capsaicin-sensitive primary afferents, is involved in the NANC inhibitory neurotransmission of the pig urinary bladder neck, producing relaxation through neuronal and muscle VIP/PACAP receptor activation.

H2S produces pig bladder neck relaxation via activation of adenosine 5'-triphosphate dependent K(+) channel and by smooth muscle intracellular Ca(2+) desensitization dependent mechanisms. H2S also promotes the release of sensory neuropeptides and cyclooxygenase-1 pathway derived prostanoids from capsaicin sensitive primary afferents via transient receptor potential A1, transient receptor potential vanilloid 1 and/or related ion channel activation.