Absence of renal circulatory autoregulation during perfusion with paraffin oil

Autoregulation of vascular flow as a function of arterial pressure was studied in isolated dog and rat kidneys, perfused serially with an oxygenated aqueous colloidal medium and with oxygenated paraffin oil. Square wave elevations in arterial pressure eleicited autoregulatory adjustments in flow within the first few seconds of elevated pressure during colloidal perfusion but not during oil perfusion of the same kidneys. Before oil perfusion, the steady state autoregulatory efficiency ratios (% flow change/% pressure change) over pressures ranging from 95 to 180 mm Hg averaged 0.37 +/- 0.13 and 0.51 +/- 0.16 (mean +/- SD) in dog and rat kidneys, respectively. During oil perfusion, the autoregulatory efficiency ratios exceeded 1.0 in every instance. Following oil perfusion, vasoactive autoregulation of colloidal perfusate flow returned, at very low organ flows. Our results do not confirm the previous findings of LEICHTWEISS, SCHRODER, and WEISS [Pflügers Arch. ges. Physiol. 293: 303 1967] concerning the presence of autoregulation during oxygenated renal oil perfusion. Our findings suggest that renal circulatory autoregulation is either primarily myogenic or else primarily dependent upon a rapidly acting tubulovascular feedback mechanism.