Regulation of hepatic function by stress-related neuropeptides in the brain

Neuropeptides have recently been recognized as new neurotransmitter and neuromodulator, and are widely distributed in the central nervous system as well as peripheral nerves. Several neuropeptides in the central nervous system are shown to act in the specific brain sites and control gastrointestinal functions through the autonomic nervous system. Recently, a relationship between central neuropeptides and hepatic function through the autonomic nervous system has been revealed using animal models. Neuropeptide Y acts in the left dorsal vagal complex, especially Y1 receptor subtype, to stimulate bile secretion. Thyrotropin-releasing hormone acts in the medulla, specially the left dorsal vagal complex, to induce a stimulation of hepatic blood flow and hepatic proliferation, and protect against experimental liver injury through vagal and cholinergic pathways. Corticotropin-releasing factor injected intracisternally elicits an inhibition in the hepatic blood flow and aggravates experimental liver injury through sympathetic and noradrenergic pathways. Further studies regarding physiological relevance of the central action of neuropeptides on specific brain sites should be performed for unraveling the underlying pathways mediating brain–liver interaction.