Changes in Renal Blood Flow, Extraction of Inulin, Glomerular Filtration Rate, Tissue Pressure and Urine Flow With Acute Alterations of Renal Artery Blood Pressure

Abstract

In anesthetized dogs one renal artery was cannulated in situ and the blood pressure to the kidney mechanically altered and maintained for periods of 7-10 minutes at levels from 20 to over 320 mm. Hg. Simultaneously measured were renal blood flow (RBF) (by recording rotameter) and the extraction of inulin (E%IN) from which were computed renal plasma flow and glomerular filtration rate (GFR). Urine flow was also measured. From perfusion pressures of approx. 20 mm. Hg, RBF, E% IN and GFR increased rapidly up to approx. 80 mm. Hg, above which all three functions remained relatively constant until perfusion pressure reached approx. 180 mm. Hg. Above 180, RBF increased rapidly, E%IN decreased, and the resulting GFR remained essentially unchanged. Flow of urine began at an avg. of 60 mm. Hg and increased exponentially, until at very high perfusion pressures the flow of urine was 25-75% of the existing GFR. The relative constancy of RBF and E%IN between 80 and 180 mm. Hg is believed to be an indication of autonomous regulation, effected by changes in tone of the afferent arterioles. Evidence suggests that distortion of the renal blood vessels resulting from increased intravascular pressure caused an increased renal tissue pressure which was primarily responsible for a diminished transfer of filtrate through the tubular wall and the consequent increase in urine flow.