Autoregulation of renal blood flow,glomerular filtration rate and renin release in conscious dogs

The relationship between renal artery pressure (RAP), renal blood flow (RBF), glomerular filtration rate (GFR) and the renal venous-arterial plasma renin activity difference (PRAD) was studied in 22 chronically instrumented, conscious foxhounds with a daily sodium intake of 6.6 mmol/kg. RAP was reduced in steps and maintained constant for 5 min using an inflatable renal artery cuff and a pressure control system.Between 160 and 81 mm Hg we observed a concomitant autoregulation of GFR and RBF with a high precision. The break off points for GRF- and RBF-autoregulation were sharp and were significantly different from each other (GFR: 80.5±3.5 mm Hg; RBF: 65.6±1.3 mm Hg;P<0.01). In the subautoregulatory range GFR and RBF decreased in a linerar fashion and ceased at 40 and 19 mm Hg, respectively.Between 160 mm Hg and 95 mm Hg (threshold pressure for renin release) PRAD remained unchanged; below threshold pressure PRAD increased steeply (average slope: 0.34 ng AI·ml^–1·h^–1· mm Hg^–1) indicating that resting renin release may be doubled by a fall of RAP by only 3 mm Hg. At the break-off point of RBF-autoregulation (66 mm Hg) renin release was 10-fold higher than the resting level.It is concluded that under physiological conditions (normal sodium diet) GFR and RBF are perfectly autoregulated over a wide pressure range. Renin release remains suppressed until RAP falls below a well defined threshold pressure slightly below the animal's resting systemic pressure. RBF is maintained at significantly lower pressures than GFR, indicating that autoregulation of RBF also involves postglomerular vessels. Our data are in agreement with the myogenic hypothesis as a basic mechanism of autoregulation.This study was supported by the German Research Foundation (FG Niere, Kr. 546/5-1, Projekt 3). A preliminary report of a part of this investigation has been presented to the Vth European Colloquium on Renal Physiology 1985 (Kirchheim et al., Renal Physiol, Basel 9:84, abstract 80, 1986)