The mechanisms of fast renal compensation

Summary The changes in blood concentration which result in the adjustment of excretion when renal functioning mass is acutely reduced have been investigated by means of paired experiments on isolated dog kidneys. One kidney was perfused with undiluted blood; the other kidney was perfused with blood supplemented with an amount of water and solutes corresponding to the amount retained after the suppression of the contralateral kidney in situ; the response was evaluated from the difference in excretion between the two organs. The results may be summarized as follows: a) the adjustment of the excretion of water, sodium, potassium and urea results from small changes in blood concentration (haematocrit, plasma proteins and solutes), in the absence of specific stimuli of extrarenal origin; b) increased urea concentration is not the major determinant of the readjustment of sodium and water excretion; c) the response is potentiated by high arterial blood pressure; d) if the load of water exceeds the load of sodium, this ion is retained by the kidney even in the presence of an osmotic load of urea; e) the changes in the blood concentrations do not provide an adequate adjustment of the excretion of phosphate; f) increased excretion per nephron results from decreased fractional reabsorption without significant change in glomerular filtration rate.