Regulatory peptide distribution in separated layers of the human jejunum

Effects of substance P and vasoactive intestinal polypeptide on contractile activity and epithelial transport in the ferret jejunum

Previous studies in the ferret demonstrated that vagal nerve stimulation induced an atropine-resistant water secretion. Substance P and vasoactive intestinal polypeptide are possible mediators of this secretory response. The objectives of this study were to investigate the in vivo effects of substance P and vasoactive intestinal polypeptide on the jejunal musculature and epithelium. Substance P caused an increase in jejunal motility, water secretion, and transmural potential difference. Cholinergic blockade did not affect the substance P-induced contractions, but did reduce the increase in transmural potential difference, suggesting an inhibition of water secretion. Vasoactive intestinal polypeptide abolished motor activity; however, it induced an increase in transmural potential difference that was atropine and tetrodotoxin resistant. By immunohistochemical methods, immunoreactive vasoactive intestinal polypeptide and immunoreactive substance P were localized to both nerve cell bodies and nerve fibers in the ferret intestine. Determination of intestinal concentrations of vasoactive intestinal polypeptide and substance P in the ferret showed concentrations of these two neuropeptides that were similar to those in human intestine and demonstrated much higher concentrations of these substances in the muscular layer than in the epithelial layer. Our data demonstrate that in the ferret substance P excites and vasoactive intestinal polypeptide inhibits jejunal motor activity. However, both peptides increase water secretion. Our results suggest that in response to vagal stimulation, neuronally released substance P or vasoactive intestinal polypeptide may participate in the atropine-resistant water secretion.

Intramural distribution of regulatory peptides in the sigmoid-recto-anal region of the human gut

The distribution of regulatory peptides was studied in the separated mucosa, submucosa and muscularis externa taken at 10 sampling sites encompassing the whole human sigmoid colon (five sites), rectum (two sites), and anal canal (three sites). Consistently high concentrations of VIP were measured in the muscle layer at most sites (proximal sigmoid: 286 (16) pmol/g, upper rectum: 269 (17), a moderate decrease being found in the distal smooth sphincter (151 (30) pmol/g). Values are expressed as mean (SE). Conversely, substance P concentrations showed an obvious decline in the recto-anal muscle (mid sigmoid: 19 (2.0) pmol/g, distal rectum: 7.1 (1.3), upper anal canal: 1.6 (0.6)). Somatostatin was mainly present in the sigmoid mucosa and submucosa (37 (9.3) and 15 (3.5) pmol/g, respectively) and showed low, but consistent concentrations in the muscle (mid sigmoid: 2.2 (0.7) pmol/g, upper anal canal: 1.5 (0.8]. Starting in the distal sigmoid colon, a distinct peak of tissue NPY was revealed, which was most striking in the muscle (of mid sigmoid: 16 (3.9) pmol/g, upper rectum: 47 (7.8), anal sphincter: 58 (14)). Peptide YY was confined to the mucosa and showed an earlier peak (upper sigmoid: 709 (186) pmol/g, mid-distal sigmoid: 1965 (484)). A clear differential distribution of regulatory peptides was thus shown in the region studied. A possible role is suggested for NPY and VIP containing nerves in the effector control of the human internal anal sphincter.