Regulation of filtration rate in sodium-depleted and -expanded dogs

Sodium balance may affect the response of single-nephron filtration rate (SNFR) to changes in renal arterial pressure (deltaRAP) when the SNFR is measured in the absence of orthograde fluid delivery from the proximal tubule. This thesis was tested in sodium-depleted and -expanded dogs given furosemide, Doca, and low- or high-salt diets, respectively. After 7 days of treatment, renal renin content was significantly greater in the sodium-depleted group (delta = 23.5 +/- 7.4 DU [dog units]/g kidney). Glomerular filtration rate and renal plasma flow were similar in both groups following changes in RAP of 29 +/- 4 and 29 +/- 3 mmHg in the sodium-depleted and -expanded groups, respectively. SNFR at high RAP was not different from SNFR at low RAP in the sodium-depleted group (delta = -0.2 +/- 4.9 nl/min) and slightly, but significantly, greater in the sodium-expanded group (delta = 7.6 +/- 2;1 nl/min). However, the response of SNFR was similar to that of whole-kidney filtration rate. Furthermore, the autoregulatory response (deltaSNFR/deltaRAP) was not significantly different between the groups but was significantly greater than the response calculated for RAP below the range studied. It is concluded that an autoregulatory response of SNFR, in the absence of orthograde fluid delivery from the proximal tubule, is observed in both sodium-depleted and -expanded dogs.