Movement of the gastrointestinal system. Parkinson’s disease affects the action of smooth (involuntary) muscle tissue such as that of the digestive system. Many people with moderate to advanced Parkinson’s have dyspha-gia (difficulty in swallowing) and chronic constipation, which reflect the slowed activity of the muscles responsible for moving food down the esophagus and through the intestines and colon. Researchers believe this occurs in part as a result of the imbalance between dopamine and acetyl-CHOLINE, two NEUROTRANSMITTERS integral to movement. It also is likely that the overall reduction in movement further slows the gastrointestinal tract; walking and physical activity are traditionally recommended for gastrointestinal problems such as constipation. As Parkinson’s erodes the ability to walk, physical activity becomes challenging if not impossible.
As well, many of the anti-parkinson’s medications taken to treat the disease’s motor symptoms adversely affect the gastrointestinal tract, causing many of the same problems and compounding their effects. As dopamine depletion in the brain progresses in advancing Parkinson’s disease, the imbalance between dopamine and acetylcholine deepens. Although there is no increase in the amount of acetylcholine, its actions intensify because there is less dopamine to counteract them. A key therapeutic line of attack in Parkinson’s disease employs the anticholinErgic medications, taken to reduce the action of acetylcholine in the brain. However, they also reduce acetylcholine levels peripherally (elsewhere in the body). This effect slows muscle response and activity throughout the body, helping to reduce tremors and rigidity. Although the slowing is an intended therapeutic effect from the standpoint of the motor symptoms of Parkinson’s, it also has unintended and undesired effects on other muscle action. See also cisapride.