Release of immunoreactive somatostatin, vasoactive intestinal polypeptide (VIP), and galanin during propulsive...

We studied the release of immunoreactive somatostatin, VIP, and galanin during net aboral propulsive complexes (NAP) in isolated, perfused, 80-cm segments of porcine ileum. Net aboral propulsive complexes were induced by controlled infusion of liquid (perfusion medium, 3.5 ml/min) into the proximal opening of the ileum segment. In response to liquid infusion, the ileum segments generated propulsive complexes rapidly propagating along the entire segment in the aboral direction, resulting in emptying of the luminal contents. The NAPs occurred with an average interval of 7 minutes. The concentrations of galanin, somatostatin, and VIP in the venous effluent, which in control experiments without luminal infusion did not change, increased significantly (by 63.6 +/- 23.7%, 43.8 +/- 31.8%, and 38.8 +/- 14.6%, respectively) during NAPs and emptying. Atropine (10(-6) mol/l) and hexamethonium (10(-5) mol/l) abolished both NAP generation and peptide responses. It is concluded that the enteric neuropeptides, somatostatin, VIP, and galanin, all of which have pronounced intestinal motor effects, may participate in the generation of net aboral propulsive complexes in the ileum of the pig, possibly mainly in descending relaxation.