Prostaglandins and brain-gut axis
Prostaglandins (PGs) have well documented physiological and pharmacological actions on the gastrointestinal (GI) tract. This communication reviews the evidence for peripheral and central nervous system (CNS) physiological actions of PGs in order to determine their role in the brain-gut axis, if any. PGs are widely distributed in nearly all cells peripherally and centrally. Laboratory and clinical evidence indicate that there is a direct relationship between altered GI physiological functions and peripheral PGs biosynthesis. Either local or parenteral administration of natural E-series PGs alters GI physiological functions particularly those relating to mucosal defense. Furthermore, the cyclooxygenase enzymes (COX), which are responsible for the PGs biosynthesis, have been localized in the brain as well as peripherally. However, increased levels of PGs in the brain have been associated with pathological processes such as inflammation, pain, fever and addiction. Although PGs have been shown to modulate CNS effects of catecholaminergic, serotoninergic and cholinergic neurons, there is no meaningful information concerning their direct central effect on GI function. The evidence for a clear physiological role of central PGs on the GI tract is not convincing. At this time, we conclude that PGs primarily manifest their activity on the GI tract by peripheral rather than by central mechanisms.