Autoregulation of Directly Measured Blood Flows in the Superficial and Deep Venous Drainage Areas of the Cat Kidney

Abstract

The renal arterial pressure was changed in steps of 25 mm Hg, or it was successively varied between two levels (100 and 150 mm Hg) to obtain four or five stable flow recordings at each level. Statistical calculations indicated that the blood flows in the two drainage areas of the cat kidney were autoregulated with equal effectiveness (whether judged from inflow or outflow rates). The flows at 100 mm Hg were approximately 95% of the flows at 150 mm Hg. To establish whether the accuracy of the method was sufficient to detect a possible nonautoregulated fraction of the arcuate flow similar in magnitude to that traversing the medulla, the flow data were compared with the flows calculated from a simple mathematical model consisting of three homogeneous compartments (outer cortical, inner cortical, and medullary), each with its own pressure-flow relationship. If the flows through all cortical glomeruli are similarly autoregulated, the experimental results are incompatible with a flow through juxtamedullary glomeruli which is proportional to pressure and constitutes 5-;7%, or more, of the total renal blood flow.

The Renal Microcirculation

“…While cortical blood flow is well autoregulated over the physiological range of renal perfusion pressure, the extent to which MBF is autoregulated is less certain. Some early experiments that examined the transit time of labeled indicators favored lack of autoregulation while other similar examinations favored its presence [2,374,1466,1467] . The renal medulla is largely perfused by postglomerular blood.…”

The renal medullary microcirculation

“…Perfusion of the renal cortex is autoregulated, however, the autoregulation of the smaller fraction of renal blood flow that reaches the medulla is uncertain. Early experiments using dye transit times favored lack of medullary autoregulation but many subsequent studies favor its presence (70)(71)(72)(73)(74)(75)(76). Recent studies in the rat suggest that the efficiency of medullary autoregulation depends upon extracellular fluid volume status.…”