An ultrasensitive method for the simultaneous determination of cyclic AMP and cyclic GMP in small-volume samples from blood and tissue

Abstract Taking advantage of the reports of Cailla et al. that succinylation of cyclic AMP and cyclic GMP causes a tremendous increase in their affinities for the antisera (8,9), a simple and ultrasensitive radioimmunoassay has been developed for the simultaneous determination of the cyclic nucleotides in a small volume of biological materials. The binding of succinylated cyclic nucleotides by their specific antibodies is so stabilized in an imidazole buffer that undiluted plasma or the concentrated extract of tissues is directly assayed for cyclic nucleotides without carrying out any prior purification, such as deproteinization of column chromatography. Thus, blood levels of cyclic AMP and cyclic GMP are readily determined in as a small volume of plasma as 50 μl. Periodical changes in the blood concentration of cyclic nucleotides in response to adrenergic and hormonal stimuli were followed in individual rats by means of this method.