THE RENAL EXCRETION OF ACETOACETATE AND 3‐HYDROXYBUTYRATE DURING ABSOLUTE FASTING

During absolute fasting with increasing ketosis the renal excretion of acetoacetate (AA) and 3-hydroxybutyrate (3-HB) has been in principle found to be identical. At low plasma concentrations the urinary excretion rate was near 0. With AA concentrations greater than approximately 0.09 mmol/1 and 3-HB concentrations greater than approximately 1 mmol/1 the urinary excretion rate of both AA and 3-HB increased rectilinearly with the plasma concentration, indicating that clearance was constant. AA/creatinine clearance ratio and 3-HB/creatinine clearance ratio increased, accordingly, from approximately 0 to an average of 0.15 and 0.19, respectively. These results are in agreement with the view that at low plasma concentrations the ketone bodies are reabsorbed almost completely, whereas an amount corresponding to about 1/5 of the filtered amount is excreted at higher plasma concentrations. Binding of ketone bodies to plasma proteins was not found in filtration studies and therefore both AA and 3-HB are apparently completely ultrafiltrable.