Urethral response during bladder contraction induced by subcutaneous bethanechol chloride: elicitation of a sympathetic reflex urethral constriction.

The responses of the urethra to bladder filling and to subcutaneous bethanechol were studied in a surgically separated bladder-urethra preparation in chloralose anesthetized cats. With the pudendal nerves cut or the neuromuscular junction blocked with gallamine, urethral closure pressure increased during bladder filling and the initial phase of the micturition contraction. It then fell spontaneously or in response to bladder emptying through a vent. With the bladder volume held constant subcutaneous bethanechol induced an increase in basal bladder pressure which culminated in a sustained (reflex) contraction. The urethral constrictor response resembled that seen during the cystometrogram; an increase during the rise in detrusor pressure and a fall during the latter part of the sustained (reflex) contraction. In both cases the urethral response was substantially depressed by hypogastric nerve transection or by intravenous prazosin, implying that the urethral responses were reflexly mediated through the sympathetic system. Intra-arterial bethanechol also produced a urethral constriction, but this response was abolished by atropine and not affected by hypogastric nerve section or prazosin. It is therefore concluded that although bethanechol can produce urethral constriction through a direct muscarinic action on the urethra, it does not do so after subcutaneous administration in a neurally intact cat. The urethral response seen after subcutaneous bethanechol administration is part of the micturition reflex complex and is sympathetically mediated.