The rationale behind seeking an association between perioperative alterations in the L-arginine/NO pathway and postoperative ileus is that NO synthesized by neuronal NOS is considered a main non-cholinergic and non-adrenergic inhibitory neurotransmitter in the gut, and NOS inhibitors have been shown to alleviate postoperative ileus in animal models [53]. Here, NOS1 is linked to ileus.