ROLE OF AUTOREGULATION IN MAINTAINING GLOMERULAR FILTRATION RATE AT LARGE URINE FLOW

The effects of large urine flow and high tubular pressure on renal blood flow (RBF) and glomerular filtration rate (GFR) were studied in dogs. In unanesthetized animals, ethacrynic acid and furosemide infused during hypotonic saline or mannitol diuresis increased urine flow to more than half of the filtered load without reducing GFR, whereas clearance of paraamino‐hippurate (CI’.VH) rose. In anesthetized dogs, ethacrynic acid and furosemide increased RBF. By stepwise renal artery constriction RBF was reduced in proportion to perfusion pressure, indicating abolished autoregulation. A similar moderate increase in RBF and abolition of autoregulation were also obtained by ureteral obstruction. In contrast, autoregulation was maintained until RBF was nearly doubled during infusion of saline or mannitol. During infusions of hypotonic solutions, CPAH increased despite reductions in serum osmolality which in renal perfusion experiments led to a fall in RBF. Conclusion: High tubular or intestitial pressure acts on the autoregulating mechanism which dilates afferent arterioles until the hydrostatic pressure difference over the glomerular membrane is reestablished. By this mechanism, RBF is increased and GFR maintained at high urine flow. Vasodilating factors may be elicited during expansion of extracellular volume, but do not affect autoregulation and are without distinct effect on GFR. © 1969 Scandinavian Physiological Society