[Gastrointestinal dysfunction has important implications for plasma L-dopa concentrations in Parkinson's disease].

Gastrointestinal motility dysfunctions including anorexia, nausea, heartburn, bloating, etc. are common and frequent complication of Parkinson's disease (PD). Degeneration of enteric nerves system is supposed to be a pathogenesis of these symptoms. Impairment of gastric emptying (GE) leads to retardation of the drug delivery from stomach to jejunum, so that PD patients with GE impairment show the delayed elevation of plasma L-dopa concentration. Disturbance of L-dopa absorption will result in wearing-off and delayed-on, and these are called motor fluctuation. In our investigation, 69% of PD patients who exhibited delayed elevation of plasma L-dopa concentration complicated GE impairment, whereas only 22% of patients with normal L-dopa level showed GE retardation (p = 0.0044, χ(2)-test). Serotonin 5-HT4 agonist and dopamine D2 antagonist are useful to improve GE impairment in PD. These drugs stimulate the postganglionic cholinergic fiber to release acetylcholine amongst the enteric nerves system and facilitate the gastrointestinal tract. Rikkunshi-to, dietary herbal medicine, is also administered to ameliorate gastrointestinal symptoms in PD. Rikkunshi-to is reported to improve erratic GE and reduce the variation of plasma L-dopa level. Recently, intestinal continuous L-dopa administration is expected as the potential solution for L-dopa induced motor fluctuation in advanced PD.