Sodium nitroprusside and guanosine 3',5'-monophosphate (cyclic GMP) inhibit stimulated phosphoinositide hydrolysis in rat cerebral cortical slices.

The combination of carbachol and 20 mM K+ greatly stimulates phosphoinositide hydrolysis in rat cerebral cortical slices. This response was inhibited by sodium nitroprusside, an activator of guanylate cyclase which elevated guanosine 3',5'-monophosphate (cyclic GMP) levels. 8-Bromocyclic GMP and the phorbol ester phorbol myristate acetate (PMA) also inhibited phosphoinositide hydrolysis, and the inhibitory effect of PMA was additive with that of sodium nitroprusside. As guanylate cyclase is Ca2+-dependent this inhibition of phosphoinositide hydrolysis by cyclic GMP may serve as a feedback modulator of the production of inositol phosphates and the ensuing rise of intracellular calcium.