Renal HCO 3 ‐ Reabsorption Is Differentially Modulated by Water Deprivation Depending on Food / Na + Intake

Although kidneys are able to perform water balance dissociated from Na + balance, hypovolemic dehydration, as seen during water deprivation (WD), modifies both. Moreover, WD can occur singly or together with food deprivation (FD) and, therefore, may differently alter such parameters. NHE3 is the major pathway for NaHCO 3 ‐ in the proximal tubule and is important to volume balance, but the effect of WD on it is not well known. The goal of this work was to determine the effect of WD on HCO 3 ‐ reabsorption (JHCO 3 ‐ ) and the role of food (FI) or Na (NaI) intake in this mechanism. Rats were kept for 24 hs with water ad libitum (CTRL) or in WD, and JHCO 3 ‐ was measured by means of stationary microperfusion. WD decreased by 34% JHCO 3 ‐ (vs CTRL), and this effect was NHE3‐dependent, since the S3226(NHE3‐inhibitor)‐insensitive component of JHCO 3 ‐ was not modulated by WD. Because NaI increases renal Na + excretion and could influence JHCO 3 ‐ , animals were kept in WD and fed with a deficient Na + diet (DNa), to determine the role of NaI on WD effect. As expected, in the absence of dietary Na + , JHCO 3 ‐ was stimulated. Moreover, despite during WD + DNa, JHCO 3 ‐ has decreased by 13% (vs DNa alone), the inhibitory effect of WD on JHCO 3 ‐ was attenuated (since WD decreased JHCO 3 ‐ by 34% when animals were fed with a CTRL diet). Because others dietary components besides Na + , may influence JHCO 3 ‐ , animals were kept in FD and WD. Although NaI was null during both, DNa and FD, JHCO 3 ‐ was not stimulated by this last condition. Besides, the observed attenuation on JHCO 3 ‐ was smaller (JHCO 3 ‐ was 13% for DNa vs DNa + WD and 26% for FD vs FD + WD). These results indicate that WD inhibits NHE3. NaI presents a central role in this inhibitory effect; however NI has also a Na + ‐independent component that inhibits JHCO 3 ‐ . Financial support FAPESP, CNPq