Sympathetic nervous system in gastrointestinal motility and secretion: Neurotransmitters, receptors and drugs

Abstract

Sympathetic nerve fibers in the gastrointestinal tract are derived from neurons in prevertebral ganglia, and terminate around intrinsic neurons of intestinal plexuses and in sphincter muscles. Sympathetic innervation of intestinal smooth muscles and mucosal cells is sparse. Noradrenaline is released from sympathetic nerve terminals, and acts via alpha and beta adrenergic receptors located on neuronal and effector cells throughout the gastrointestinal tract. Sympathicus exerts tonic activity on the intestinal blood flow and secretions, but not on motility. However, sympathetic stimulation results in the inhibition of propulsive activity of the gut. In extreme conditions, stress, pain, abdominal irritation, intestinal obstruction induce excessive activation of sympathetic inhibitory pathways in the gut, and may cause adynamic ileus, which can be relieved by alpha-2 receptor blocking drugs, and possibly by beta-blockers. Pharmacological effects of drugs acting on adrenergic mechanisms vary along the gastrointestinal tract and between species. Their therapeutical use is rather limited and in many instances controversial.