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We read the case report of Malouf and Kamm (Gut 2001;48:728–9) with interest. However, we disagree with some of the science and suggest an alternative explanation for their findings.
Firstly, there is much data to suggest that sympathetic innervation of the internal anal sphincter is in fact excitatory. The paper that they cite1 (from their own institution) showed that noradrenaline, the principal postganglionic neurotransmitter of the sympathetic nervous system, caused contraction of this tissue in vitro. Operative in vivo studies of presacral nerve stimulation have indeed been contradictory, showing both an increase2 and decrease3 in internal anal sphincter tone; this probably reflects little more than differences in stimulation parameters. However, sympathetic blockade effected either by infusion of the α adrenoceptor antagonist phentolamine4 or by high spinal anaesthesia5 produces a significant fall in internal anal sphincter tone. This is evidence …
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- Case report