The urinary bladder is a smooth muscle organ the function of which is to collect and store urine at low intravesical pressures, and then periodically to expel urine via a highly co-ordinated sustained contraction (Levin et al. 1990a; Anderson, 1993; Steers, 1994; Zderic et al. 1996a). The urethra functions to maintain continence during bladder filling, and then to provide a low-resistance pathway during micturition. The control of lower urinary tract function is through the autonomic nervous system. During bladder filling, the sympathetic nervous system is active and this produces an increase in tension of the bladder base and urethra via activation of a-adrenergic receptors, and relaxation of the bladder body via activation of ß-adrenergic receptors. In addition, sympathetic activity inhibits parasympathetic ganglionic transmission via postsynaptic sympathetic fibres which act upon a2-type receptors located in the ganglia. Micturition is mediated via the co-ordinated parasympathetic activation of cholinergic muscarinic receptors of the bladder body with the simultaneous inhibition of [alpha]-adrenergic tone of the bladder neck and urethra (Steers, 1994; Zderic et al. 1996a). Active urethral relaxation mediated by nitric oxide may also play a role during micturition (Anderson, 1993; Steers, 1994; Zderic et al. 1996a).