Gastrointestinal Effects of Opioids

Although opioid alkaloids have been used as antidiarrheals for centuries, only during the last decade has it been recognized that endogenous opioid pep tides produce dual effects on gastrointestinal motility and intestinal chloride and gastric acid secretion. μ-, κ-, and δ-opioid receptors are involved and mediate opioid effects on neurons and smooth muscle cells by at least two different cellular mechanisms. The gastrointestinal opioid system physiologically interacts with several gastrointestinal neurotransmitters and serves as a neuromodulatory system. This chapter will discuss the current knowledge on gastrointestinal opioid effects, from the esophagus to the anal sphincter.