Functional Evidence of Vasomotor Control by Tachykinins in the Heat Dissipating Tissues of the Canine Nose and Face

Abstract

In contrast to man and non-furred mammals, in which excessive body heat is dissipated by evaporation of the skin, furred mammals mainly depend on evaporative heat loss via the ventilated mucous membranes of mouth, tongue and nose. Considering that this respiratory mechanism also serves to condition the inspired air, a precise neurogenic vasomotor control of convective heat transfer from the core to these mucous surfaces (especially the nose) is a prerequisite for the provision of adequate perfusion rates over a wide range. While the role of sympathetic vasoconstrictor and parasympathetic vasodilator efferents in nasal blood flow control has been clarified, a local vasomotor control by afferent fibers, is still debated. Nevertheless, the innervation of the nasal and facial vasculature by substance P (SP) — immunoreactive afferent nerve fibers, their relationship with the sensory, in particular the trigeminal system, and the relaxing potency of SP on vasomotor tone, suggest the involvement of this peptide in locally induced vasomotor changes. In addition to local axon reflex SP-release, SP-fibers may influence parasympathetic efferents at the sphenopalatine ganglionic level. This type of vasomotor control is assumed to be important in connection with allergic and hyperreactive disorders of the nose (1). In recent studies it has been demonstrated that the various requirements for the adjustments of nasal blood flow under physiological conditions are met by the arteriovenous anastomoses (AVA) at relatively stable capillary flow (CAP-FLOW) (2). Physiological control of vasomotor tone of these vessels is not solely governed by symapthetic adrenergic but also by parasympathetic cholinergic efferents (3). Since the latter are associated with SP fibers, it appears reasonable also to suggest their co-action, at least in a modulatory way.