Development and evaluation of an immunoenzymometric assay for the chicken progesterone receptor

A specific and sensitive immunoenzymometric assay (IEMA) was developed for measuring the quantity of chicken progesterone receptor (PR) in tissue cytosol. The assay uses two monoclonal antibodies to the PR. One is used to capture the PR. The second (labelled with biotin) reacts first with the captured receptor and subsequently with avidin-labelled horseradish peroxidase to provide an enzymatic end-point. The method has a determination range from 0.3 to 60 pmol/l. Intra- and interassay coefficients of variation were 3.7% and 9.0% respectively. The assay can be performed with equal results as a rapid (3 h) or an overnight procedure. The IEMA is convenient, especially for signal measurement and the calculation of results. No ultracentrifugation of samples is needed, since the IEMA can be performed on low-speed cytosol samples. Assay results correlated well (r = 0.927) with those obtained by the conventional ligand-binding assay used in our laboratory. Similar results were obtained with the IEMA and the ligand-binding assay after exposure of cytosol samples to increased temperatures: at 20 degrees C the PR remained stable for the 4-h period examined, whereas at 37 degrees C almost complete degradation of the PR was observed in 30 min. Being more than 100 times as sensitive as the ligand-binding assay, the IEMA enabled the quantification of PR for the first time in such tissues as the bursa and small intestine even of immature animals.