Screening of cattle urine samples for the presence of beta-agonists with a functional test: some preliminary results

A new procedure based on the measurement of biological effects has been developed for the determination of residues of beta-agonists, such as clenbuterol, in urine. A multi-chamber superfusion apparatus containing isolated trachea strips from guinea pigs was used to detect smooth muscle relaxation induced via beta 2-adrenoceptor activation. The trachea tissue was pre-contracted with metacholine. Urine samples were extracted using a solid-phase column containing reversed-phase and anion-exchange materials. Extracts were introduced into the superfusion apparatus via flow injection. The intensity and response of relaxation are dependent on the type and concentration of the beta-agonist introduced. The sensitivity of the assay for clenbuterol in calf urine is about 1 microgram l-1. This methodology in the present form is especially suitable for survey screening analysis for several types of samples. An extensive validation of the procedure is performed to determine the range of analytes that can be detected, the possibilities of analysing urine samples obtained from mature cattle or other animal species and the influence of cross-reacting substances.