Measurement of tachykinin-induced salivation in conscious rats

A method of quantitatively measuring tachykinin-induced salivation in conscious, male, Sprague-Dawley rats is described. Salivation is quantified by determining the weight of a preweighed, absorbant foam cube after it has been used to swab the oral cavity of a tachykinin challenged rat. Salivation is induced by intravenous (i.v.) injection of sialogogues (μg/kg) via the lateral tail vein. Measurements are made immediately after injection. Substance P (Sub.P), Sar⁹, Met (O₂)¹¹Substance P (Sar⁹ Sub.P), a selective neurokinin (NK) 1 receptor agonist, Physalaemin and Eledoisin are equipotent sialogogues as determined by this method. Neurokinin A (NKA), the endogenous NK2 receptor agonist, is 0.27 (0.14–0.46) times as potent as Sub.P, while (Suc-[Asp⁶,MePhe⁸]Substance P(6–11), (senktide), a selective NK3 receptor agonist, only induced salivation at 300 μg/kg. Acetylcholine (Ach) is only 0.006 (0.002–0.012) times as potent as Sub.P. Treatment with the neurokinin antagonist [D-Arg¹, D-Trp^7,9Leu¹¹]-Substance P (spantide) dose-dependently inhibits Sub.P stimulated salivation. Atropine dose-dependently inhibits Ach induced salivation but is inactive against Sub.P-induced salivation. These data are consistent with literature values and indicate that this method provides a simple, quantitative model, free of any possible anesthetic side effects, for the measurement of neurokinin stimulated salivation and the assessment of potential neurokinin antagonists in vivo.