Formation and excretion of branched-chain acylcarnitines and branched-chain hydroxy acids in the perfused rat kidney

alpha-Keto[U-14C]isovalerate, alpha-keto[U-14C]isocaproate and alpha-keto[U-14C]beta-methylvalerate are metabolized in the perfused kidney. Labelled 3-hydroxyisobutyrate, 3-hydroxyisovalerate, 2-methyl-3-hydroxybutyrate, branched-chain amino acids, branched-chain acylcarnitines and lactate are formed. Hydroxy acids and acylcarnitines are excreted preferentially in the urine, whereas the branched-chain amino acids are preferentially excreted in the perfusate. There is no accumulation of (U-14C)-labelled alpha-keto acids or labelled metabolites in the kidney during perfusion. (-)-Carnitine accumulates rapidly in the kidney when it is added to the perfusate. A high kidney carnitine level enhances the excretion of carnitine esters in the urine.