IJUP08 - Universidade do Porto

Purinergic signalling in a model of overactive urinary bladder
Nuno Silva 1 , Miguel Faria 1 , Vítor Cavadas 2 and Paulo Correia-de-Sá 1
1Laboratório de Farmacologia e Neurobiologia, UMIB, Instituto de Ciências Biomédicas de Abel
Salazar (ICBAS) – Universidade do Porto (UP).
2 Serviço de Urologia, Hospital Geral de Santo António (HGSA), Porto, Portugal.
The mechanisms for relaxation of the bladder during the filling phase, and for initiation of the
micturition reflex, are incompletely understood. Normal bladder contraction in humans is
mediated mainly through stimulation of muscarinic cholinergic receptors in the detrusor
muscle (for a review, see [1]). Atropine-resistant (noncholinergic, nonadrenergic [NANC])
contractions have been reported in normal human detrusor. The atropine-resistant purinergic
(P2X1) component of human bladder contraction may be increased to 40% in elderly people
and patients with bladder pathologies (e.g. hypertrophic and neurogenic bladders, interstitial
cystitis) [2,3]. The bladder epithelium releases ATP in response to mechanical stimuli (and to
chemical irritants), and it is hypothesized that ATP released from the serosal surface of the
urothelium during bladder filling stimulates P2X3-containing receptors on suburothelial
sensory nerve fibres, thus signaling information about urinary bladder filling. Thus, we aim at
investigating the mechanisms involved in the control of ATP release from the urothelium, to
prompt for new targets (e.g. mechanosensory pathway) for pharmacological manipulation of
bladder overactivity.
Experiments were carried out, at 37ºC, in urethane-anaesthetized (25% solution, initial dose:
1.0−1.2 g/kg, maintenance dose: 0.1 g/kg), spontaneously breathing male Wistar rats (300−450
g). The dome of the urinary bladder was catheterized using a three-barrel cannula for
continuous measurement of intraluminal pressure. The micturition reflex was evoked by
bladder distension induced by intravesical infusion of saline (0.05 ml/min). Respiratory tidal
volume, bladder pressure, ECG and pelvic nerve activity were continuously displayed on
computer screen via a PowerLab data acquisition system (Chart 5, v.4.2 software; AD
Instruments, USA). Urine samples before and after bladder filling were assayed for ATP
content using the luciferin-luciferase bioluminescence assay (Enliten ATP kit, Promega, USA).
Bladder overactivity was induced by intravesical infusion of acetic acid (0.2-1%, v/v in saline).
Bladder filling is normally followed (within a few minutes) by an increase in the
electrophysiological activity (firing rate and amplitude) of the pelvic nerve, which occurs
synchronously to large amplitude spontaneous contractions of the detrusor – micturition reflex.
Acetic acid (0.2-1%, for 15 min) concentration-dependently decreased the time (ranging from
67 to 81% of control) and the pressure threshold (ranging from 58 to 85% of control) for the
appearance of the first isovolumetric contraction. The magnitude of isovolumetric contractions
tends to increase proportionally to the concentration of acetic acid infused into the bladder.
During the micturition reflex, we observed an increase (52±7%, n=5) in urinary ATP, which
was significantly (P