Opioids play an important role in chronic pain relief and work by binding to mu-receptors
in the central nervous system, but they also bind to mu-receptors
in the gastrointestinal tract, which can result in patients suffering from OIC.
Animal studies have demonstrated that opioid mu-receptors
are concentrated in the dorsal horn of the spinal cord, where the bladder afferents merge (Coggeshall & Carlton, 1997; Singh, Agarwal, Batra, Kishore, & Mandal, 2008).