APERIA, ANITA C., C. G. OVE BROBERGER, AND &GRID SEDERLUND. Relationship between renal artery perfusion pressure and tubular sodium reabsorption. Am. J. Physiol. 220(5): 1205-1212. 1971.In the in situ perfused dog kidney perfusion pressure was gradually increased from 110 to 325 mm Hg. Renal blood flow remained stable until perfusion pressure exceeded 225-240 mm Hg, the glomerular filtration rate over the entire pressure range studied. There was a direct relationship between renal artery perfusion pressure and fractional sodium excretion both in hydropenia and in water diuresis. In hydropenia, fractional sodium excretion and free water reabsorption increased with elevation of renal artery perfusion pressure up to 160 mm Hg. Beyond this range free water reabsorption declined and finally became negative while the fractional sodium excretion continued to increase. In water diuresis, fractional distal tubular sodium reabsorption was found to be more inhibited when urine flow was increased by increment in perfusion pressure than by intravenous mannitol load. Albumin infusion into the renal artery abolished the high-pressure natriuresis except in chlorothiazide-treated dogL. c This supports the hypothesis that tubular sodium reabsorption is controlled by physical forces.