Feedback control of glomerular filtration rate in isolated, blood-perfused dog kidneys

Micropuncture studies were done in isolated, blood-perfused dog kidneys to investigate the intrarenal nature of tubuloglomerular feedback regulation of nephron filtration rate. Collections were made at early proximal tubular sites during alterations in flow through the loop of Henle to elicit the feedback response. Renal blood flow in the 10 isolated kidneys averaged 4 ml/ min-g kidney after an initial vasoconstriction. Filtration rate was 0.52 +/- 0.12 ml/min-g kidney for the period 90-120 min, but progressively fell after 120 min, as did fractional sodium reabsorption and PAH extraction. The feedback regulation of nephron filtration rate was demonstrated during the first 3 hrs of perfusion even with subnormal renal function. The feedback response expressed as the percent reduction of early proximal flow rate when loop of Henle flow was elevated from 0 to 45 nl/min was 41.3 +/- 4.5 (for the first 90 min), 35.3 +/- 7.5 (90-120 min), 24.3 +/- 6.8 (120-150 min), and 26.6 +/- 7.7% (150-180 min). After 180 min, the feedback response was no longer demonstrated. These results show that feedback-induced changes in nephron filtration rate are achieved in the absence of nervous system influences.