CATECHOLAMINE INTERFERENCE WITH ENZYMATIC DETERMINATION OF NONESTERIFIED FATTY-ACIDS IN 2 COMMERCIALLY AVAILABLE TEST KITS

We present evidence that catecholamines, which are commonly used to st imulate lipolysis in adipose tissue in vitro, interfere with the enzym atic determination of nonesterified fatty acid (NEFA) in two commercia lly available kits. Measurement of a 100 mu mol/L standard with the Wa ke ''NEFA C'' test kit was 60% inhibited by 100 mu mol/L norepinephrin e and was completely inhibited by 100 mu mol/L isoproterenol or by 1 m mol/L norepinephrine or epinephrine. Measurement with the Boehringer M annheim ''Free Fatty acids, Half-micro test'' was completely inhibited by 100 mu mol/L norepinephrine and was also affected by concentration s as low as 0.1 mu mol/L. We propose that this effect is due to the ca techolamines interfering with a step common to the two kits, the gener ation of hydrogen peroxide and oxidation of a chromagen; furthermore, this interference appears to be stoichiometric. We also give details o f an alternative in-house method, which does not depend on the generat ion of hydrogen peroxide and is not affected by catecholamines.