EFFECT OF TACHYKININS ON THE NEED-FREE SODIUM-INTAKE OF FEMALE RATS -A CONTINUOUS INTRACEREBROVENTRICULAR INFUSION STUDY

The present study investigated the effect of 24-h continuous ICV infus ion of four different tachykinins on the enhanced need-free sodium int ake induced by previous repeated sodium depletions in female rats. Fem ale rats were employed because, in response to sodium depletions, they develop a higher need-free sodium intake than male rats. The followin g tachykinins were used: eledoisin, substance P (SP), [Sar(9),Met(O-2) (11)]SP and [Asp(5,6),MePhe(8)]SP(5-11), also referred to as NH2-senkt ide, all at the same doses of 300 or 600 ng/h x 24 h. Food pellets, wa ter, and 3% NaCl sodium solution were freely available. Eledoisin and NH2-senktide were more potent than SP in reducing the need-free sodium intake. On the other hand, [Sar(9),Met(O-2)(11)]SP had no effect. Non e of the tachykinins employed completely blocked the intake. Water int ake was reduced, but this reduction was apparently a consequence of re duced intake of hypertonic sodium deride solution, because at the same doses TKs did not inhibit water intake in a single-bottle test. Food intake remained unchanged at either dose used. These findings confirm previous studies in which pulse injection of the same drugs potently i nhibited sodium intake. They also demonstrate that tachykinins endowed with high affinity for the NK3 receptor are the most potent in inhibi ting sodium intake. Furthermore, these findings indicate that the tach ykinins reduce the need-free sodium intake only during the infusion pe riod, indicating that in these conditions they do not evoke either ave rsion for salt, or toxic consequences in the follow-up period.