RENAL AUTO-REGULATION OF BLOOD-FLOW AND FILTRATION-RATE IN THE RABBIT

Electromagnetic flow techniques and inulin clearance were used to determine the autoregulatory capabilities of the rabbit kidney in vivo. Renal blood flow was measured in 13 animals over a renal perfusion pressure range of 40-110 mm Hg. Normal renal blood flow averaged 3.2 .+-. 0.3 ml min per g kidney and was efficiently autoregulated above a renal artery pressure of 75 mm Hg. For every 10 mm Hg renal pressure change above 75 mm Hg renal blood flow changed only 0.96%. Renal perfusion pressure was reduced from 102 .+-. 3 to 74 .+-. 2 mm Hg in 6 animals. Over this pressure range glomerular filtration rate was not significantly decreased and averaged 4.2 .+-. 0.5 ml/min at high pressure compared to 4.0 .+-. 0.5 ml/min at low perfusion pressure. Results show that the rabbit kidney autoregulates renal blood flow and glomerular filtration rate efficiently above 75 mm Hg. This range of autoregulation compares well with the autoregulatory range of the dog. In the autoregulatory range the rabbit and the rat appear to autoregulate with equal efficiency but that the rabbit kidney begins to autoregulate at a lower perfusion pressure than the average of approximately 100 mm Hg usually found in the rat.