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)