Determination of Guanosine 3',5'-Monophosphate in Tissues and of Guanyl Cyclase in Rat Intestine

Abstract A method for the assay of cyclic guanosine 3',5'-monophosphate has been applied to the determination of the nucleotide in tissues. Concentrations of cyclic GMP were determined in various tissues from several animal phyla. These levels were in most cases much lower than cyclic AMP, but an insect, the cricket, contained more cyclic GMP than cyclic AMP. Cyclic GMP was found in all rat tissues examined, and the upper small intestine contained relatively large amounts. The contents of the small intestine also were found to contain cyclic GMP, with that from the lower part containing more. Theophylline, an inhibitor of cyclic nucleotide phosphodiesterase, elevated the level of cyclic GMP in rat small intestine. This suggests a rapid turnover of the nucleotide in this tissue. An enzyme system which catalyzed the formation of cyclic GMP from GTP was demonstrated in small intestine. This enzyme required Mn++ for maximal activity and was inhibited by ATP. It was apparently different from adenyl cyclase.