Somatostatin-immunoreactive nerve fibers in close association with capillaries in the small intestine

Somatostatin as an Active Substance in the Mammalian Enteric Nervous System

Somatostatin (SOM) is an active substance which most commonly occurs in endocrine cells, as well as in the central and peripheral nervous system. One of the parts of the nervous system where the presence of SOM has been confirmed is the enteric nervous system (ENS), located in the wall of the gastrointestinal (GI) tract. It regulates most of the functions of the stomach and intestine and it is characterized by complex organization and a high degree of independence from the central nervous system. SOM has been described in the ENS of numerous mammal species and its main functions in the GI tract are connected with the inhibition of the intestinal motility and secretory activity. Moreover, SOM participates in sensory and pain stimuli conduction, modulation of the release of other neuronal factors, and regulation of blood flow in the intestinal vessels. This peptide is also involved in the pathological processes in the GI tract and is known as an anti-inflammatory agent. This paper, which focuses primarily on the distribution of SOM in the ENS and extrinsic intestinal innervation in various mammalian species, is a review of studies concerning this issue published from 1973 to the present.

Growth-regulatory effects of sensory neuropeptides, epidermal growth factor, insulin, and somatostatin on the non-transformed intestinal epithelial cell line IEC-6 and the colon cancer cell line HT 29

A non-transformed small-intestinal cell line from the rat (IEC-6) and a human colon cancer cell line (HT 29) were examined for their trophic response to sensory neuropeptides. Substance P, neurokinin A (NKA), calcitonin gene-related peptide (CGRP), vasoactive intestinal peptide (VIP), and peptide YY (PYY) were tested. Epidermal growth factor (EGF), insulin, and somatostatin-14 were also used. Interaction studies were performed on IEC-6 cells by combining EGF or insulin with somatostatin-14. The sensory neuropeptides had no effect either on IEC-6 cell growth and DNA synthesis or on HT29 cell growth. EGF and insulin stimulated cell growth and DNA synthesis in IEC-6 cells and cell growth in HT 29 cells in a dose-dependent fashion. Somatostatin-14 had no effect either alone or in combination with EGF or insulin on IEC-6 cell growth and DNA synthesis. HT 29 cell growth was inhibited by somatostatin-14 only in the presence of serum with a maximal and significant response at 10(-7) M. Our observations suggest that the sensory neuropeptides do not exert a direct growth-regulatory effect either on IEC-6 cells or on HT 29 cells. Somatostatin, however, inhibits serum-induced HT 29 cell growth but does not interfere directly with the proliferative effect of serum, EGF, or insulin on IEC-6 cells in this model.

Somatostatin modulates vascular sympathetic neurotransmission in the rabbit ear artery

Somatostatin-like immunoreactivity was localised immunohistochemically in perivascular nerves in the rabbit central ear artery. Whilst somatostatin had no direct action on this vessel, it significantly inhibited noradrenaline-induced, but not alpha, beta-methylene ATP-induced, vasoconstriction. Somatostatin also inhibited contractions elicited by electrical field stimulation showing greater effect at low (16 Hz) compared with high (64 Hz) frequencies, and inhibited the release of tritiated noradrenaline in a concentration-dependent manner. These results confirm that somatostatin is a neuroregulatory peptide, and suggest that it is modulating vascular sympathetic cotransmission of the rabbit central ear artery by acting both prejunctionally to inhibit transmitter release, and postjunctionally to reduce the action of noradrenaline.