Determination of cyclic 3'-5'-adenosine monophosphate in plasma by RIA methods in the presence of EDTA.
Calcium ions definitively increase the ability of cyclic 3',5'-adenosine monophosphate (cAMP) to bind to its antibody. In contrast, ethylenedinitrolotetra-acetic acid as its disodium salt (EDTA) shows a dose-dependent inhibition of the binding of cAMP to its antibody. The less sensitive protein binding methods are not affected by EDTA. This is inconvenient, because the EDTA-plasmas can be stored frozen without breakdown of cAMP, but are unsuitable for sensitive radioimmunoassays. The aim of this investigation was to determine how calcium ions and EDTA affect the binding of cAMP to its antibody. Based on these results, we describe an alternative procedure for commercial RIA methods for the determination of cAMP in EDTA-plasma. The almost complete inhibition of the hapten-antibody reaction by EDTA can be abolished by adding an equivalent concentration of calcium ions to the reaction medium together with trichloroacetic acid. Thus a simple and rapid procedure was found for the storage of plasma and for the determination of plasma cAMP.
D002118:Calcium; D000242:Cyclic AMP / Q000097:blood*; D004492:Edetic Acid; D005260:Female; D006801:Humans; D011247:Pregnancy; D011863:Radioimmunoassay / Q000379:methods*
D004492:Edetic Acid; D000242:Cyclic AMP; D002118:Calcium