PACAP 38 is involved in the non-adrenergic non-cholinergic inhibitory neurotransmission in the pig urinary bladder neck

Aims: To investigate the role played by pituitary adenylate cyclase activating polypeptide 38 (PACAP 38) in the non-adrenergic non-cholinergic (NANC) neurotransmission of the pig urinary bladder neck. Methods: Urothelium-denuded bladder neck strips were dissected and mounted in organ baths containing a physiological saline solution (PSS) at 37 degrees C and gassed with 5% CO, and 95% O-2, for isometric force recording. The relaxations to transmural nerve stimulation (EFS) or PACAP 38 were performed on strips precontracted with 1 mu M phenylephrine (PhE). EFS experiments were carried out in the absence and the presence of guanethidine (10 mu M), atropine (0.1 mu M), and N-G-nitro-L-arginine (L-NOARG, 100 mu M), to block noradrenergic neurotransmission, muscarinic receptors, and nitric oxide (NO) synthase, respectively. Results: EFS (2-16 Hz, 1 ms duration, 20 see trains, 75 mA current output) evoked frequency-dependent relaxations which were reduced by the VIP/PACAP receptor antagonist PACAP (6-38) (3 mu M), and by the neurotoxin of the capsaicin-sensitive primary afferents capsaicin (10 mu M), and abolished by the neuronal voltage-activated Na+ channel blocker tetrodotoxin (TTX, 1 mu M). The vasoactive intestinal peptide (VIP) receptor antagonist [Lys(1), Pro(2,5), Arg(3,4), Tyr(6)]-VIP (3 mu M) failed to modify the EFS-induced relaxations. PACAP 38 (1 nM- 1 mu M) induced concentration-dependent relaxations which were reduced by PACAP (6-38), TTX and by the neuronal voltage-gated Ca2+ channel inhibitor omega-conotoxin GVIA (omega-CgTX, 1 mu M). Conclusions: The results suggest that PACAP 38, mainly released from capsaicinsensitive 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.