EFFECTS OF THE SELECTIVE TACHYKININ NK3 RECEPTOR AGONIST NH2-SENKTIDEON INTRAORAL INTAKE AND TASTE REACTIVITY RESPONSES ELICITED BY NACL IN SODIUM-REPLETE RATS

Our previous studies have shown that i.c.v, injections of the selectiv e tachykinin NK3 receptor agonist [Asp(5,6),MePhe(8)]substance P(5,11) , also referred to as NH2-senktide (NH2-SENK), inhibit salt intake in rats in a two-bottle intake test. The present study evaluated the effe ct of i,c,v, injections of NH2-SENK on intraoral intake and taste reac tivity responses elicited by intraoral infusions of water or NaCl solu tions (0.03, 0.15, 0.25 and 0.5 M) in sodium-replete rats. The effect of NH2-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 NH2-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 NH2-SENK reduced the intraoral intake of 0.25 acid 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 H-2-S ENK on salt intake is dependent on the concentration of the NaCl solut ion offered; moreover, the intraoral intake data suggest that the effe ct of NH2-SENK on salt intake may be exerted to a large extent on the consummatory processes of salt ingestion. NH2-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 passiv e dripping during the first min of intraoral infusion of 0.15, 0.25 an d 0.5 M, but not of water or of 0.03 M NaCl, This finding suggests tha t NH2-SENK elicits a prompt alteration of taste mechanisms for salt, w hich may account for its antinatriorexic action.