Autoregulation of plasma flow in the isolated perfused rat kidney.

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Abstract
Autoregulation of renal plasma flow, by which flow remains constant despite changes in perfusion pressure, was studied in the isolated, perfused kidney of the rat. Autoregulation did not occur in preparations perfused with a protein-free medium consisting of a balanced ionic solution resembling rat plasma in which 3% polyvinylpyrrolidone replaced plasma proteins, changes in perfusion pressure over the normal autoregulatory range 100-150 mmHg produced a corresponding and linear change in venous outflow and no consistent change in renal vascular resistance. Addition of human serum (5%, vol/vol) to the medium restored autoregulation; changes in perfusion pressure in the range 100-150 mmHg resulted in a stable plasma flow and a linear change in renal vascular resistance. Addition of bovine serum albumin (3 g/l) to the protein-free medium restored autoregulation to a similar degree. In kidneys perfused with the protein-free medium, sensitivity of the renal vasculature to the vasoconstrictor drugs epinephrine and angiotensin II was only 1/40 the level seen in those kidneys perfused with media containing serum or albumin. In the isolated, perfused kidney, autoregulation of plasma flow was not dependent on the presence of the globulin, angiotensinogen, in the perfusion medium. The failure of autoregulation in kidneys perfused with a protein-free medium was attributed to the rapid decline in sensitivity of the vascular smooth muscle to constrictor stimuli.