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 NK 3 receptor agonist, and [Sar 9 , Met(O 2 ) 11 ]-substance P (Sar Met; 100, 200 ng), an NK 1 receptor agonist, on normal (gastric fistula closed) and sham drinking (gastric fistula open) of hypertonic NaCl by sodium-deficient rats were compared. Intraventricular injections of Sar Met had no effect on NaCl intake in either condition. Injections of 100 ng and 200 ng SENK caused an equal suppression of NaCl intake in the 2 fistula conditions. The latency to drink was not affected, but the initial lick rate was significantly lower and decayed more rapidly after 100 ng SENK than after saline or 25 ng SENK. The results show that (a) the tachykinin subtypes are not equally involved in the control of need-induced salt intake; (b) negative feedback from the stomach and distal gastrointestinal tract is not required for intraventricular injections of SENK to suppress sodium appetite; (c) the activation of NK 3 receptors decreases the oral excitatory influence of hypertonic NaCl in sodium-deficient rats.