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PubMed1987

VIP release from enteric nerves is independent of extracellular calcium.

The release of endogenous vasoactive intestinal polypeptide (VIP) from enteric nerves of isolated rat ileum and the role of extracellular calcium on the release mechanism have been investigated. Evaluation of simultaneous release of endogenous acetylcholine (ACh) and adenosine 5'-triphosphate (ATP) from enteric nerves was used to establish the reliability of the technique. Electrical field stimulation of the ileal preparation induced an increase in the release of endogenous ACh, ATP and VIP. The evoked, but not the basal, release of these substances was blocked by tetrodotoxin (TTX), indicating that the release was a result of nerve stimulation. However, while increase in release of ACh and ATP during nerve stimulation was suppressed in Ca2+-free medium and by the addition of the Ca2+ channel blocker cadmium, nerve-mediated VIP release was unaffected. Further, while K+-depolarization induced release of ACh and ATP from the ileal preparations, it did not lead to an increase in the release of VIP. These results demonstrate that, unlike ACh and ATP release, release of endogenous VIP from enteric nerves is independent of extracellular calcium. The implications of these results in terms of the mechanism of transmitter release in the gastrointestinal tract are discussed.

Acetylcholine↗

PubMedDate not supplied

Long-term sensory denervation does not modify endothelial function or endothelial substance P and nitric oxide synthase in rat mesenteric arteries.

Mesenteric endothelial cell function and immunoreactivity for substance P and nitric oxide synthase (NOS) were examined in control rats and rats treated with capsaicin as neonates to destroy primary afferent nerves. Endothelial vasodilator function was examined pharmacologically in the methoxamine raised-tone isolated perfused mesenteric arterial bed. Endothelial immunoreactivity for substance P and NOS was examined at the ultrastructural level by electron-microscopic immunocytochemistry. The endothelium-dependent vasodilators acetylcholine and adenosine 5'-triphosphate elicited dose-dependent relaxations which were not different between control and capsaicin-treated rats. Dose-dependent relaxations to endothelium-independent vasodilators, calcitonin gene-related peptide and sodium nitroprusside, were also unchanged by capsaicin treatment. Positive staining for substance P was detected in 25% of endothelial cells in both control and capsaicin-treated rats. Positive staining for NOS was detected in 50% of endothelial cells in control rats, and this was not changed by capsaicin treatment. These results confirm that endothelial substance P is independent of substance P contained in sensory nerves. Long-term sensory denervation does not produce changes in endothelium-dependent or -independent relaxation, or in the number of endothelial cells showing positive labelling for substance P and NOS in rat mesenteric arteries.

Animals↗