Attomole sensitive radioimmunoassay for cyclic GMP.

The sensitivity of the radioimmunoassay for cyclic GMP has been improved to readily detect attomole (200-300) amounts of the nucleotide in tissue extracts. The improved sensitivity has been achieved by using a high specific radioactivity [125I] cyclic GMP 2'O-succinyl tyrosine methyl ester (2200 Ci/mmole) as labeled antigen in conjunction with acetylation of the cyclic GMP in the samples as well as by using a selected cyclic GMP antibody. The high specific [125I] cyclic GMP 2'O-succinyl tyrosine methyl ester was prepared radiochemically pure by radioiodination of cyclic GMP 2'O-succinyl tyrosine methyl ester and purification using HPLC. The new attomole sensitive cyclic GMP radioimmunoassay is simple to perform and fast and has been applied with success to determine attomole quantities of cyclic GMP in cultured smooth muscle cells and AG 1523 fibroblasts.