Distinction between oral and parenteral application of 19-nortestosterone by residue analysis in kidney fat from veal calves using high-performance liquid chromatography and enzyme immunoassay.

Kidney fat samples from animals either untreated or after different treatments with 19-nortestosterone (NT) were cleaned up and NT-17 beta and 19-norandrostenedione (NA) were purified using high-performance liquid chromatographic (HPLC) systems that allowed their complete separation from other steroids and interfering physiological compounds. HPLC fractions and urine samples were analysed by an enzyme immunoassay that measures both steroids equally well (antigen: NT-17 beta-hemisuccinate-bovine serum albumin). In samples from untreated animals no NT metabolites were detectable (less than 10 pg/g NT-17 beta and less than 10 pg/g NA in fat; less than 0.25 pg/ml NT-17 beta + NT-17 alpha in urine). After adding NT to animal feed the urine became positive, whereas in the fat no residues were detectable. After different injections of NT both the fat and urine were positive. Only after parenteral application did free steroids enter the circulation and adipose tissues.