The influence of tubulo-glomerular feedback on the autoregulation of filtration rate in superficial and deep glomeruli.

Single nephron glomerular filtration rate (SNGFR) of superficial and juxtamedullary nephrons were measured at normal and reduced perfusion pressure in the left kidney of young Sprague Dawley rats. Perfusion pressure was lowered by constricting the aorta proximal to the branching of the left renal artery. The influence of the tubulo-glomerular feedback mechanism on SNGFR was quantitated by measuring SNGFR during intact and interrupted urine flow to the macula densa region. By using a modified Hanssen technique, SNGFR was measured under free-flow conditions. In other experiments, the urine flow to the distal nephron was blocked by a micropuncture technique, which was used for collection of the tubular fluid for measuring the filtration rate. All nephron populations autoregulated SNGFR from 70-80 to 130 mmHg, which was the upper limit of this investigation, when urine flow throughout the nephron was intact. The autoregulation in this pressure range was lost when tubular fluid was prevented from reaching the distal nephron. It was shown that the influence of negative feedback on SNGFR by the macula densa mechanism at normal blood pressure is greater in deep nephrons than in superficial ones.