cGMP: ProductsGuanosine 3, 5-cyclic monophosphate (cGMP) is formed via the action of guanylate cyclase on GTP. cGMP is present at levels typically 10-100 fold lower than cAMP in most tissues. A variety of stimuli including acetylcholine, insulin, oxytocin, serotonin, and histamine will cause an increase in cGMP levels. Various stimulators of guanylate cyclase (e.g. vasodilators) as well as peptides that relax smooth muscle also increase cGMP concentrations.