Effects of the selective tachykinin NK 3 receptor agonist NH 2-senktide on intraoral intake and taste reactivity responses elicited by NaCl in sodium-replete rats

Abstract

Our previous studies have shown that i.c.v. injection of the selective tachykinin NK 3 receptor agonist [Asp 5,6,MePhe 8]substance P(5,11), also referred to as NH 2-senktide (NH 2-SENK), inhibit salt intake in rats in a two-bottle intake test. The present study evaluated the effect of i.c.v. injections of NH 2-SENK on intraoral intake and taste reactivity responses elicited by intraoral infusions of water or NaCl solutions (0.03, 0.15, 0.25 and 0.5 M) in sodium-replete rats. The effect of NH 2-SENK on the intake of 0.03, 0.15 and 0.25 M NaCl solutions and of water was also evaluated in a two-bottle intake test. In this test, 31 ng/rat of NH 2-SENK significantly reduced the intake of 0.15 and 0.25 M NaCl, but not that of water or of 0.03 M NaCl. The dose of 31 ng/rat of NH 2-SENK reduced the intraoral intake of 0.25 and 0.5 M NaCl, while 125 ng/rat reduced the intraoral intake of 0.15, 0.25 and 0.5 M NaCl; neither dose reduced the intraoral intake of water or of 0.03 M NaCl. Taken together, these findings indicate that the effect of NH 2-SENK on salt intake is dependent on the concentration of the NaCl solution offered; moreover, the intraoral intake data suggest that the effect of NH 2-SENK on salt intake may be exerted to a large extent on the consummatory processes of salt ingestion. NH 2-SENK, 31 or 125 ng/rat, altered taste reactivity responses shortly after the beginning of the intraoral infusion. The most peculiar effect was an increase in passive dripping during the first min of intraoral infusion of 0.15, 0.25 and 0.5 M, but not of water or of 0.03 M NaCl. This finding suggests that NH 2-SENK elicits a prompt alteration of taste mechanisms for salt, which may account for its antinatriorexic action.