Determination of plasma cyclic AMP with automated radioimmunoassay system (Gamma-flo)

We have adapted the Gamma-flo automated radioimmunoassay system to analyze for cyclic 3',5'-AMP in plasma. Direct analysis of plasma samples was not possible due to an interfering substance(s) in plasma. Evidence suggested that the interfering substance is human serum albumin. An efficient, relatively simple method was developed by applying the acetylation procedure to ultrafiltrates of plasma samples and utilizing the Gamma-flo system for rapid radioimmunoassay (50 samples per hour) of cyclic AMP content in the filtrates. Coefficient of variation within assays averaged 3% and interassay coefficient of variation was 4.7%. Recovery of cyclic AMP from plasma into the ultrafiltrate ranged from 93 to 100%. Increments of cyclic AMP added to plasma were recovered linearly up to approximately 60 pmol/ml, the highest concentration tested.