In vitro evidence for the participation of intestinal opioids in the control of peristalsis in the guinea pig small intestine

Summary The influence of naloxone on the peristaltic reflex of isolated segments of various parts of the guinea pig small intestine was examined. The narcotic antagonist (–)naloxone (2×10^–7M), but not its stereoisomer (+)naloxone, increased the frequency of peristaltic waves in ileal segments by an average of 12%. In addition, it decreased the length and number of peristalsis-free intervals during periods of elevated intraluminal pressure. Thus, it increased over-all-peristaltic-activity by 25–60%, dependent upon intraluminal pressure.Segments from the duodenum and the proximal or distal jejunum displayed no statistically significant increase of peristalsis after naloxone application.Despite differences in over-all-peristaltic-activity, opiate receptor blockade by naloxone induced changes of a comparable magnitude in preparations from both fetal and adult animals. Neither pregnancy nor enforced prolonged work of the isolated segments enhanced the influence of naloxone relative to normal adult animal preparations.It is concluded that intestinal opioids participate in the control of peristalsis in preparations taken from normal animals rather than being activated only in special in vivo or in vitro circumstances such as pregnancy or fatigue, or at a particular phase of life, for example, during fetal stages.