Synthetic NPY exerts vasoconstricto

Synthetic NPY exerts vasoconstrictor actions in the pulp in the low nanomolar range and, this effect is resistant to -adrenoceptor blockade. Compared to the effect of Noradrenaline (NA), Neuropeptide Y causes a more sustained vasoconstriction that lasts for several minutes after the end of an intra-arterial infusion. It is therefore plausible that NA and NPY act in concert in initiating and maintaining an appropriate vascular tone in the pulp. (8)

The dental pulp is a soft tissue of mesenchymal origin which houses a number of tissue elements including nerves, vascular tissue, connective fibers, ground substance, interstitial fluid, odontoblasts, immunocompetent cells and other cellular components. (1) Sympathetic innervation of the dental pulp terminates as free nerve endings and innervates the arterioles. (2) An interaction between exogenous irritants and defensive host cells results in the release of neuropeptides such as Substance P (SP), Calcitonin Gene Related Peptide (CGRP), Vasoactive Intestinal Polypeptide (VIP), Neurokinin A (NKA), Neuropeptide Y (NPY). Neuropeptides are proteins generated from somatosensory and autonomic nerve fibers after tissue injury. (3)

Increased production and release of these neuropeptides play an important role in initiating and propagating pulpal inflammation. (4) During inflammation, sprouting of nerve fibers is associated with increased expression of neuropeptides such as SP or CGRP closely surrounding the areas of inflammation or abscess. (5) Denervation of the inferior alveolar nerve depletes the pulp of its content of SP and CGRP, but not of NPY, and also increases the magnitude of pulpal necrosis following experimental pulpal exposures. (5)

Neuropeptides contribute to inflammatory processes via number of mechanisms where SP, CGRP and VIP function as potent vasodilators and NPY as a vasoconstrictor. (6) Vasodilatation following infusion of SP or VIP in the pulp is associated with a transient increase in pulpal blood flow that was followed by a substantial and prolonged reduction in pulpal blood flow. Neuropeptides also reduce the threshold of pain in the pulp, accounting for symptoms associated with certain cases of pulpitis in children. (7)
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SP was the first neuropeptide to be detected in dental pulp. SP, CGRP and NKA coexist in the same nerve fibers in the pulp and originate from the trigeminal ganglion. (8)

Pulpal vasodilatation is markedly reduced after systemic administration of a specific SP antagonist or Somatostatin. Thus, Somatostatin, present in trigeminal nerve, inhibits the release of SP and reduces the concomitant vasodilation in the pulp following inferior alveolar nerve stimulation. (8)
- See more at: http://archive.ispub.com/journal/the-internet-journal-of-dental-science/volume-8-number-2/role-of-neuropeptides-in-pulpal-pathosis-an-overview.html#sthash.gjgNf3RH.dpuf