Distal tubular feedback in the autoregulation of single nephron glomerular filtration rate

Abstract

Renal clearance and recollection micropuncture experiments were conducted to evaluate the possible role of a distal tubular feedback mechanism in the phenomenon of renal autoregulation in dogs. Single nephron glomerular filtration rate (SNGFR) was measured from collection sites in both the proximal (proximal SNGFR) and distal tubules (distal SNGFR). Single nephron autoregulatory behavior was assessed by evaluating the response of SNGFR to a reduction in renal arterial pressure imposed by means of an aortic constrictor. Whole kidney function was evaluated by parallel measurements or renal blood flow and inulin clearance. Whole kidney autoregulation was observed when renal arterial pressure was decreased from 141±3 (SE) mm Hg to 101±2 mm Hg; renal blood flow and GFR were not significantly altered from control values of 3.76±0.2 ml/min/g and 0.69±0.04 ml/min/g kidney weight, respectively. In 11 autoregulating preparations, proximal transit time was likewise unchanged from the control value of 26±2 s, suggesting that the superficial nephrons also participated in the autoregulatory response. However, proximal SNGFR decreased significantly from 88±7 nl/min, a reduction which was proportional to the decrease in arterial pressure. In 14 dogs in which both proximal SNGFR and distal SNGFR were measured at control blood pressure (136±5 mm Hg), distal SNGFR was 47±4 nl/min, a value significantly lower than that for proximal SNGFR (79±6 nl/min). In contrast to the results based upon proximal collections, distal SNGFR was not significantly altered following aortic constriction (44±5 nl/min vs. 47±5 nl/min) therefore exhibiting autoregulation on association with that observed for the whole kidney.