Paradoxical resistance to adrenolytic agents of filled-stimulated bladder base of rabbit

Isolated circularly or longitudinally oriented strips from anterior or posterior rabbit bladder base were tested for responsiveness to agonists and sensitivity of field stimulation-induced responses to antagonists. Results were compared to the regional distribution of adrenergic and cholinergic nerves, determined histochemically. Greater norepinephrine-induced responses in posterior than in anterior strips reflect denser noradrenergic innervation in posterior base. Longitudinal strips responded better to carbachol than circular strips, but no orientation-related differences in cholinergic nerve density or muscle mass were noted. Field stimulation-induced contractions were largely resistant to phenoxybenzamine (0.03 μM) and guanethidine (100 μM) and slightly reduced by phentolamine (2.6 μM). Atropine (0.4 μM) reduced maximum responses by 25 to 75%. The resistance to guanethidine suggests that the ineffectiveness of phenoxybenzamine is not due solely to atypical post synaptic receptors. Inaccessibility of the synaptic cleft to guanethidine is unlikely because the vas deferens, which possesses close contacts, was sensitive to guanethidine. Neurotransmission in bladder base may be partially nonadrenergic, noncholinergic in nature. A question arises concerning the functional significance of the noradrenergic nerves in bladder base.