Inhibition of cell dehydration-induced drinking by tachykinins: evaluation of possible renal effects accounting for the long-lasting inhibition.

Central injection of the tachykinins (TKs) neurokinin A (NKA), eledoisin (ELE), and kassinin (KASS) produced long-lasting inhibition (up to 6 h) of drinking induced by subcutaneous hypertonic NaCl, while substance P (SP) and physalaemin (PHYS) evoked short-lasting effects. The hypothesis that water retention or increased Na+ excretion by the kidney (induced by TKs) may reduce the need for water ingestion was tested. The results obtained both in urine collection experiments and in nephrectomized rats showed that the duration of the effect of NKA, ELE, and KASS is not due to water retention or increased Na+ excretion by the kidney. The effect of NKA, but not that of ELE and KASS, was shortened by nephrectomy, even though NKA did not modify urine volume or Na+ excretion. Indomethacin pretreatment, like nephrectomy, reduced the duration of the NKA effect, suggesting that renal prostaglandins are involved in it. On the other hand, the long-lasting effect of the three TKs cannot be easily explained in terms of slow metabolic degradation, particularly for NKA. Alternatively, it might be hypothesized that these TKs produce a modification of osmoreceptor function lasting well beyond the life of the peptide, and/or that they produce Na+ loss through emunctories different from the kidney.