Development, validation and implementation of a receptor based bioassay capable of detecting a broad range of β-agonist drugs in animal feedingstuffs

A bioassay was developed for the detection of a broad range of β-agonist compounds in animal feeds. A solubilised β2-adrenoceptor was utilised as the binding protein in the assay. This protein was found to be highly stable when stored at 80 °C. The assay was developed and initially validated to determine the sensitivity and relative selectivity against a panel of commonly used β-agonist compounds. It was also shown that when β-agonists were present as cocktails in samples a pronounced synergistic effect could be measured. The method was further validated according to EC Decision 2002/657 and proved capable of detecting 250 ng clenbuterol equivalents per gram of sample. This is well below the quantities normally associated with β-agonist medicated feeds. The β2-adrenoceptor used in the study only failed to bind the compound zilpaterol, raising doubts as to whether this compound is a true β2-adrenergic drug.