INHIBITION OF ISOTONIC SODIUM-CHLORIDE INTAKE IN THE RAT BY SELECTIVETACHYKININ AGONISTS

The present study investigated the effect of the central injection of selective tachykinin (TK) agonists on the need-free intake of 0.9% NaC l in rats. Isotonic NaCl was offered for 60 min between 1800 and 1900 h); water was offered for 4 h between 1800 and 2200 h). The TK agonist s were injected into the third ventricle just before access to fluids. The NK3-selective agonists [Asp(5,6),MePhe(8)]substance P(5-11) and S ucc[Asp(6),MePhe(8)]substance P(6-11), as well as the NK1-selective ag onist [Sar(9), Met(O-2)(11)]substance P, markedly reduced salt intake, the threshold dose for their effects being 5 ng/rat. The NK2-selectiv e agonist GR64349 reduced salt intake only at 500 ng/rat. At the dose of 31.2 ng/rat, neither the NK1 nor the NK3 agonists inhibited water i ntake, when water was the only fluid offered (between 1800 and 2200 h) , or modified food intake in food-deprived rats. The present study sho ws that a) TKs inhibit not only the need-induced salt intake, but also the need-free intake of isotonic saline, b) this effect is behavioral ly selective, and c) the effect is apparently mediated by NK1 and NK3 receptors. The finding that TKs suppress salt intake in a large variet y of experimental conditions supports the idea that the antinatriorexi c effect of TKs is independent of the physiological and hormonal statu s of the animal. It is hypothesized that TKs might modify taste sensit ivity or the hedonic evaluation of the salty taste.