1.   It has been recognised for over a century that the internal anal sphincter relaxes in response to rectal distension, a phenomenon called the rectanal inhibitory reflex.

2.   They descend from the rectum to the internal anal sphincter and do not use the classical neurotransmitter substances, acetylcholine and noradrenaline.

3.   It has been identified as a neurotransmitter in the gastrointestinal tract, and has been implicated in nerve mediated relaxation of the internal anal sphincter.

4.   Burleigh previously reported similar actions for N-monomethyl-L-arginine and L-arginine on eurogenic relaxation in human internal anal sphincter smooth muscle.

5.   Internal anal sphincter relaxation increased in amplitude and duration in all spinal patients and normal controls as the rectum was distended intermittently with increasing volumes.

6.   There was no relationship between the level of the spinal lesion and the responses of the internal anal sphincter to rectal distension.

7.   In normal subjects, the internal anal sphincter showed anal pressure increases upon deflating the rectal baloon that exceeded the predistending values.

8.   Giant contractions were always associated with enhanced internal anal sphincter relaxation and induced spontaneous balloon evacuation in nine patients.

9.   Stimulation of the sympathetic nerves is known to increase internal anal sphincter tone and inhibit colorectal contraction.

10.   The rectoanal inhibitory reflex was measured using the threshold for internal sphincter relaxation.