Differential effects of intraventricular injections of tachykinin NK1 and NK3 receptor agonists on normal and sham drinking of NaCl by sodium-deficient rats

The effects of lateral ventricular injections of succinyl-[Asp(6), N-Me-Phe (8)]-substance P (SENK; 25, 100, 200 ng), a tachykinin NK3 receptor agonist , and [Sar(9), Met(O-2)(11)]-substance P (Sar Met; 100, 200 ng), an NK1 rec eptor agonist, on normal (gastric fistula closed) and sham drinking (gastri c fistula open) of hypertonic NaCl by sodium-deficient rats were compared. Intraventricular injections of Sar Met had no effect on NaCl intake in eith er condition. Injections of 100 ng and 200 ng SENK caused an equal suppress ion of NaCl intake in the 2 fistula conditions. The latency to drink was no t affected but the initial lick rate was significantly lower and decayed mo re rapidly after 100 ng SENK than after saline or 25 ng SENK. The results s how that (a) the tachykinin subtypes are not equally involved in the contro l of need-induced salt intake; (b) negative feedback from the stomach and d istal gastrointestinal tract is not required for intraventricular injection s of SENK to suppress sodium appetite; (c) the activation of NK3 receptors decreases the oral excitatory influence of hypertonic NaCl in sodium-defici ent rats.