OBSERVATIONS ON THE FUNCTION OF THE BLADDER NECK AND URETHRA IN THE DOG

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Abstract
SUMMARY: Observations have been made of voiding in 10 dogs in response to direct bladder filling, and intravenous injection of carbachol or bethanechol before and after section of the urethra at the bladder neck.The isolated bladder is seen to be continent, and similar emptying pressures before and after urethral section at the bladder neck indicate that the primary functional sphincter of the bladder is in this region, and the urethra is unnecessary to maintain continence in the normal dog.The effects of carbachol and bethanechol are compared and it was found that in high doses carbachol causes distension of the posterior urethra with retention of urine due apparently to spasm of the external sphincter. When increasing doses of bethanechol were administered, the bladder emptied normally. This difference of action is probably due to the marked nicotinic effect possessed by carbachol.After division of the neck of the bladder both carbachol and bethanechol caused a vigorous detrusor contraction with a large rise in intravesical pressure, and complete urinary retention in five dogs. This observation is believed to be significant and is in accordance with Woodburne's (1960) hypothesis that longitudinal muscle fibres passing through the internal meatus into the urethra are responsible for opening the neck of the bladder.