Adrenergic relaxations in an in situ urinary bladder model evoked by stimulation of sensory pelvic and pudendal nerves in the rat

Urinary bladder dysfunction might be related to disturbances at different levels of the micturition reflex arc. The current study aimed to further develop and evaluate a split bladder model for detecting and analysing relaxatory signalling in the rat urinary bladder. The model allows for discrimination between effects at the efferent and the afferent side of the innervation. In in vivo experiments, the stimulation at a low frequency (1 Hz) of the ipsilateral pelvic nerve tended to evoke relaxation of the split bladder half (contralateral side; −1.0 ± 0.4 mN; n = 5), in contrast to high frequency-evoked contractions. In preparations in which the contralateral pelvic nerve was cut the relaxation occurred at a wider range of frequencies (0.5–2 Hz). In separate experiments, responses to 1 and 2 Hz were studied before and after intravenous injections of propranolol (1 mg/kg IV). The presence of propranolol significantly shifted the relaxations into contractions. Also, electrical stimulation of the ipsilateral pudendal nerve evoked relaxations of similar magnitude as for the pelvic stimulations, which were also affected by propranolol. In control in vitro experiments, substances with β-adrenoceptor agonism, in contrast to a selective α-agonist, evoked relaxations. The current study shows that the split bladder model can be used for in vivo studies of relaxations. In the model, reflex-evoked sympathetic responses caused relaxations at low intensity stimulation. The involvement of β-adrenoceptors is supported by the sensitivity to propranolol and by the in vitro observations.