“…There is evidence that nitric oxide (NO) is an important inhibitory neurotransmitter in the internal anal sphincter (IAS) and the circular and longitudinal muscle layers of the rectum [7,8]. This simple molecule is a short-lived free radical, which has a number of physiologic functions including nonadrenergic-noncolinergic neurotransmission, and has emerged as a potent biological mediator and neurotransmitter in the central and peripheral nervous system [9].…”