ABSTRACT
Vasoactive intestinal polypeptide (VIP) was isolated from extracts of porcine small intestine in the early 1970s. Somatostatin exerts an extraordinary range of physiological effects in the gut including VIP, gastrin, cholecystokinin, glucagon and secretin. Studies of the interactions of other endogenous control systems with opioid actions suggest that the opioids take part in a complex network of interactions within the enteric nervous system ultimately resulting in ordered intestinal motility. The excitatory effect of naloxone on distention-induced peristalsis is blocked by desensitization of the intestine to serotonin. Galanin acts directly on longitudinal smooth muscle of rat jejunum. It induces tonic and superimposed phasic contractile activity. A number of bioactive peptides with similar structures have been isolated from amphibian skin, mammalian gastrointestinal tract and porcine spinal cord. Secretin is released from endocrine cells in the small intestine. Secretin stimulates pancreatic secretion and bile flow, but it inhibits gastric acid secretion.
