Autoregulation of nephron filtration rate in the dog assessed by indicator-dilution technique

Micropuncture studies were conducted in anesthetized dogs to evaluate single nephron glomerular filtrate rate (SNGFR) and SNGFR autoregulation when assessed by means of an indicator-dilution technique (SNGFRID), which does not require interruption of distal volume delivery. In 18 dogs, control renal arterial pressure was 124 +/- 11 mmHg (SD), renal blood flow (RBF) was 185 +/- 58 ml/min, and whole kidney GRF was 37 +/- 7 ml/min. SNGFRID averaged 57 +/- 15 nl/min and was significantly lower than SNGFR determined on the basis of total collections (SNGFRTC) from proximal tubules (75 +/- 17 nl/min). However, SNGFRID was not significantly different from the overall average SNGFR of 62 +/- 12 nl/min estimated from whole kidney GFR and the total number of glomeruli (613,000 +/- 74,000). In 10 animals, renal arterial pressure was reduced to an average of 94 +/- 8 mmHg; whole kidney autoregulation was highly efficient and average RBF and GRF remained within 1 and 3% of their control values. Likewise, SNGFRID was not significantly altered at 52 +/- 17 and 52 +/- 16 nl/min. In contrast, SNGFRTC decreased significantly from 72 +/- 17 to 51 +/- 13 nl/min. These results indicate that the indicator-dilution technique provides a reliable assessment of SNGFR and allows the manifestation of single nephron autoregulatory behavior. They provide further support for the hypothesis that maintenance of distal volume delivery may be a necessary aspect of the autoregulation phenomenon.