ISLET CONTENTS OF CYCLIC 3′,5′-GUANOSINE MONOPHOSPHATE UNDER CONDITIONS WHICH AFFECT THE CYCLIC 3′,5′-ADENOSINE MONOPHOSPHATE

Abstract

The sensitivity of the radioimmunoassay for c[cyclic]GMP was considerably increased by previous 2''-O-succinylation of the nucleotide. The basal content of cGMP in .beta.-cell-rich pancreatic islets isolated from ob/ob-mice was similar to that of cAMP, i.e., about 3 .mu.mol/kg dry weight. Extracellular Ca2+ was a prerequisite for maintaining this amount of cGMP. The islet cGMP differed from cAMP in being only slightly enhanced or not affected at all when the islets were exposed to high concentrations of glucose, the sulfhydryl reagents chloromercuribenzene-p-sulfonic acid and iodoacetamide, or the potent phosphodiesterase inhibitor 3-isobutyl-l-methylxanthine. The data suggest that the turnover rate for cGMP is much slower than that for cAMP in the pancreatic .beta.-cells. The interrelationships between the 2 cyclic nucleotides do not seem to fit into a simple pattern of antagonism.