The effect of intracerebroventricular hypertonic infusion on sodium appetite in rats after peritoneal dialysis

Sixty minute peritoneal dialysis (PD) against isotonic glucose decreased sodium concentration [Na+] in serum and cerebrospinal fluid (CSF) to 14% and 7% of their initial values, respectively. About 3 to 4 hours after PD, [Na+] began to increase slowly, reaching the initial level 24 hr afterwards. Central restoration of Na+ was made by infusing isotonic or hypertonic fluid into the 3rd brain ventricle (3BV) of rats at different times after dialysis. Continuous infusion (1 microliter/hr) of artCSF, 150 mM Na+, from -1 to 24 hr after PD decreased sodium intake as compared with uninfused control or control receiving Na+-free infusate or distilled water. Hypertonic central sodium infusions (1 microliter/hr) administered from -1 to 8 hr after PD, did not modify sodium intake; however an infusion made from 8 to 24 hr or from 16 to 24 hr post-dialysis decreased sodium intake by 38% and 67%, respectively. The volumes of sodium ingested were compared with those of the same animal infused with CSF 150 mM Na+. The results suggest that the fall in CSF [Na+] after sodium depletion by itself does not seem to be a critical factor in the onset of specific sodium appetite.