Measurements of nephron filtration rate in the rat with and without occlusion of the proximal tubule

Bartoli, Ettore; Earley, Laurence E.
January 1973
Kidney International;Jan1973, Vol. 3 Issue 1, p372
Academic Journal
The influence of inter- rupting flow of proximal tubular fluid on nephron filtration rate (NFR) was investigated in the rat kidney by comparing values For NFR in the same nephron by the technique of tubular occlusion and total collection with a new technique, employing dilution of a perfused indicator, which does not require occlusion of the tubule or complete collection of tubular fluid. There was no significant difference between values for NFR obtained by the two methods. NFR was 30.2 ± 16.9 nl/min when measured by perfusion technique, 13.6 ± 16.3 by total collection in the same 28 proximal tubules, P> 0.00. This is in contrast to the conclusion reached by others that interrupting flow during total collection from proximal tubules activates a feedback mechanism which elevates NER. NFR was then measured twice in the same nephron by total collection from the distal tubule and either the indicator dilution method or total collection from the proximal tubule. In paired measurements NFR was frequently lower when measured by total collection from the distal tubule suggesting that collections at that site could have been incomplete. This was verified by finding that recoveries of 125I-iothalamate or ³H-inulin perfused into the early proximal tubule were lower (83 ± 32%) when total collections were made from the distal tubule than when collections were made from the proximal tubule (101 ± 13%). When a revised method for sealing the distal tubular puncture site was used, recoveries of perfused markers were equal in proximal and distal tubules. Using this revised method for collecting distal tubular fluid NFR was measured twice in the same nephron by total collection from distal and proximal tubule: there was no significant difference between the two values, the mean difference being - 0.4 ± 11.7 %. The results do not indicate that delivery of tubular fluid beyond the proximal tubule influences NFR under the conditions of the present experiments.


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