Density of substance P, vasoactive intestinal polypeptide and somatostatin-containing nerve fibers in the ageing small intestine of the rats.

Immunoelectron microscopic investigations were carried out to study the substance P, vasoactive intestinal polypeptide (VIP) and somatostatin immunoreactive nerve elements in the wall of the small intestine. In young and old animals a large number of immunoreactive nerve fibers were found in all layers of the small intestine. They were observed closely to the epithelial cells, to the blood vessel basement membrane and to the smooth muscle cells and in some cases they were observed in a synapse with other unlabelled nerve fibers. On the other hand, in the senile animals very few immunoreactive nerve fibers were observed, calculated for a 100 micron2 tissue area. In the senile animals the overall number of nerve fibers was decreased in comparison to the young and old animals and most of them were in degeneration. This change could be the cause of the changes in the senescence-related epithelial transport processes and furthermore, of the modifications of the overall intestinal motility of the gastrointestinal tract, resulting in the age-dependent transit rates.